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{{Английская Википедия/Панель перехода}}
{{short description|Team field sport}}
{{about|the American variation of gridiron football||American football (disambiguation)}}
{{Good article}}
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{{use American English|date=December 2013}}
{{Use mdy dates|date=February 2023}}
{{Infobox sport
| name       = American football
| image      = Larry Fitzgerald catches TD at 2009 Pro Bowl.jpg
| imagesize  = 250 
| caption    = [[Larry Fitzgerald]] (in blue) catches a pass while [[Cortland Finnegan]] (in red) plays defense at the [[2009 Pro Bowl]].
| nickname   = {{hlist|[[Football (word)|Football]]|[[gridiron football|gridiron]]}}
| first      = [[1869 Princeton vs. Rutgers football game|November 6, 1869]]<br />[[New Brunswick, New Jersey]], United States<br />([[Princeton Tigers football|Princeton]] vs. [[Rutgers Scarlet Knights football|Rutgers]])
| contact    = [[Contact sport#Full-contact|Full]]
| team       = 11 (both teams may [[Free substitution|freely substitute]] players between downs)
| category   = {{hlist|[[Team sport]]|[[ball game]]}}
| equipment  = {{plainlist|
* [[Ball (gridiron football)|Football]]
* [[Football helmet]]
* [[Padding|Pads]] ([[Shoulder pads (sport)|shoulder]], thigh, [[Knee pads|knee]], and optionally [[elbow pads]])}}
| venue      = [[#Field and equipment|Football field]] (rectangular: 120 yards long, {{frac|53|1|3}} yards wide)
| union      = [[International Federation of American Football]]
| glossary   = [[Glossary of American football]]
| country/region = Worldwide (most popular in North America)<!---According to [[Template:Infobox sport]], this section is supposed to list ALL geographic areas the sport is present in the broadest possible terms. Do not change this.--->
| olympic    = [[Demonstration sport|Demonstrated]] at the [[American football at the 1904 Summer Olympics|1904]] and [[American football at the 1932 Summer Olympics|1932 Summer Olympics]], [[flag football]] at the [[2028 Summer Olympics]]
| IWGA       = Invitational sport at [[American football at the 2005 World Games|2005]], [[American football at the 2017 World Games|2017]], and [[Flag football at the 2022 World Games|2022 (flag football)]] Games
}}

'''American football''' (referred to simply as '''football''' in the United States and Canada), also known as '''[[gridiron football]]''',{{refn|group=nb|The terms "[[gridiron football]]", "gridiron", and "grid" are sometimes used as synonyms for American football,<ref>[https://www.macmillandictionary.com/us/dictionary/american/gridiron "Gridiron"] {{Webarchive|url=https://web.archive.org/web/20171107025727/https://www.macmillandictionary.com/us/dictionary/american/gridiron |date=November 7, 2017}}, ''[[Macmillan English Dictionary for Advanced Learners|MacMillan Dictionary]]''</ref> as well as in a broader sense that includes [[Canadian football]].<ref>{{cite encyclopedia |url=https://www.britannica.com/EBchecked/topic/212839/gridiron-football |title=gridiron football (sport) |encyclopedia=Britannica Online Encyclopedia |publisher=britannica.com |access-date=July 13, 2010 |archive-url=https://web.archive.org/web/20100614053218/https://www.britannica.com/EBchecked/topic/212839/gridiron-football |archive-date=June 14, 2010 |url-status=live  }}</ref>}} is a [[team sport]] played by two teams of eleven players on a rectangular [[American football field|field]] with goalposts at each end. The [[offense (sports)|offense]], the team with possession of the oval-shaped [[Ball (gridiron football)|football]], attempts to advance down the field by [[Rush (gridiron football)|running]] with the ball or [[Forward pass#Gridiron football|passing]] it, while the [[Defense (sports)|defense]], the team without possession of the ball, aims to stop the offense's advance and to take control of the ball for themselves. The offense must advance at least ten yards in four [[Down (gridiron football)|downs]] or plays; if they fail, they [[turnover on downs|turn over]] the football to the defense, but if they succeed, they are given a new set of four downs to continue the [[Glossary of American football#drive|drive]]. Points are scored primarily by advancing the ball into the opposing team's [[end zone]] for a [[touchdown]] or kicking the ball through the opponent's goalposts for a [[field goal]]. The team with the most points at the end of a game wins.

American football evolved in the United States, originating from the sports of [[association football|soccer]] and [[rugby football|rugby]]. The first American football match was played on [[1869 New Jersey vs. Rutgers football game|November 6, 1869]], between two college teams, [[Rutgers Scarlet Knights football|Rutgers]] and [[Princeton Tigers football|Princeton]], using rules based on the rules of soccer at the time. A set of rule changes drawn up from [[1880 college football season|1880]] onward by [[Walter Camp]], the "Father of American Football", established the [[snap (gridiron football)|snap]], the [[line of scrimmage]], eleven-player teams, and the concept of downs. Later rule changes legalized the [[forward pass]], created the [[neutral zone (gridiron football)|neutral zone]], and specified the size and shape of the football. The sport [[Comparison of American and Canadian football|is closely related]] to [[Canadian football]], which evolved in parallel with and at the same time as the American game, although its rules were [[Burnside rules|developed independently]] from those of Camp. Most of the features that distinguish American football from rugby and soccer are also present in Canadian football. The two sports are considered the primary variants of [[gridiron football]].

American football is the most popular [[sport in the United States]] in terms of broadcast viewership audience. The most popular forms of the game are [[Professional football (gridiron)|professional]] and [[college football]], with the other major levels being [[high school football|high-school]] and youth football. {{as of|2022}}, nearly 1.04&nbsp;million high-school athletes play the sport in the U.S., with another 81,000 college athletes in the [[National Collegiate Athletic Association|NCAA]] and the [[National Association of Intercollegiate Athletics|NAIA]].<ref name=":0">{{Cite web |date=2023-07-25 |title=Football by the Numbers |url=https://footballfoundation.org/news/2023/7/25/football-by-the-numbers.aspx |access-date=2024-01-11 |website=National Football Foundation |language=en}}</ref> The [[National Football League]], the most popular American professional football league, has the [[List of sports attendance figures#Top leagues in average attendance|highest average attendance of any professional sports league in the world]]. Its championship game, the [[Super Bowl]], ranks among the most-watched club sporting events in the world. In 2022, the league had an annual revenue of around $18.6&nbsp;billion,<ref>{{Cite web |title=NFL revenue 2022 |url=https://www.statista.com/statistics/193457/total-league-revenue-of-the-nfl-since-2005/ |access-date=2024-01-11 |website=Statista |language=en}}</ref> making it the most valuable sports league in the world.<ref>{{Cite web |last=Ozanian |first=Mike |title=The World's 50 Most Valuable Sports Teams 2023 |url=https://www.forbes.com/sites/mikeozanian/2023/09/08/the-worlds-50-most-valuable-sports-teams-2023/ |access-date=2024-01-11 |website=Forbes |language=en}}</ref> Other professional and amateur leagues exist worldwide, but the sport does not have the international popularity of other American sports like [[baseball]] or [[basketball]]; the sport maintains a following in Mexico, Brazil, Canada, Europe, and Japan.

==Etymology and names==
{{Main|Football (word)|l1=''Football'' (word)}}

In the United States, American football is referred to as "football".<ref name="Football Or Soccer? What's In A Name?">{{cite web|last=Peralta|first=Eyder|title=Football Or Soccer? What's In A Name?|url=http://www.npr.org/blogs/showmeyourcleats/2010/06/10/127738094/football-or-soccer-what-s-in-a-name|publisher=[[NPR]]|access-date=April 19, 2014|date=June 10, 2010|archive-date=October 1, 2012|archive-url=https://web.archive.org/web/20121001073932/http://www.npr.org/blogs/showmeyourcleats/2010/06/10/127738094/football-or-soccer-what-s-in-a-name|url-status=live}}</ref> The term "football" was officially established in the rulebook for the [[1876 college football season]], when the sport first shifted from soccer-style rules to rugby-style rules. Although it could easily have been called "rugby" at this point, Harvard, one of the primary proponents of the rugby-style game, compromised and did not request the name of the sport be changed to "rugby".<ref>Nelson 1993, pp. 15, 22.</ref> The terms "[[Gridiron football|gridiron]]" or "American football" are favored in English-speaking countries where other types of [[Football (word)|football]] are popular, such as the United Kingdom, Ireland, New Zealand, and Australia.<ref name="'In the six' and football's other strange Americanisms">{{cite news|url=https://www.bbc.co.uk/news/magazine-22633980|title='In the six' and football's other strange Americanisms|last=Geoghegan|first=Tim|date=May 27, 2013|work=[[BBC News]]|access-date=June 28, 2013|archive-url=https://web.archive.org/web/20130609180830/http://www.bbc.co.uk/news/magazine-22633980|archive-date=June 9, 2013|url-status=live}}</ref><ref name="Living off the grid: American football in coastal Australia">{{cite web|url=http://www.abc.net.au/local/stories/2012/06/13/3524011.htm|title=Living off the grid: American football in coastal Australia|last=Huntsdale|first=Justin|date=June 13, 2012|publisher=[[Australian Broadcasting Company]]|access-date=June 28, 2013|archive-url=https://web.archive.org/web/20131028235508/http://www.abc.net.au/local/stories/2012/06/13/3524011.htm|archive-date=October 28, 2013|url-status=live}}</ref>

==History==
{{Main|History of American football|American football in the United States}}
{{History of American football}}

===Early history===
American football evolved from the sports of [[rugby football|rugby]] and [[Association football|soccer]]. Rugby, like American football, is a sport in which two competing teams vie for control of a ball, which can be kicked through a set of goalposts or run into the opponent's goal area to score points.<ref name="The basics of rugby union">{{cite news|title=The basics of rugby union|url=http://news.bbc.co.uk/sport2/hi/rugby_union/rules_and_equipment/4200680.stm|publisher=[[BBC]]|access-date=April 19, 2014|date=September 2005|archive-url=https://web.archive.org/web/20140301181407/http://news.bbc.co.uk/sport2/hi/rugby_union/rules_and_equipment/4200680.stm|archive-date=March 1, 2014|url-status=live}}</ref>

What is considered to be the first American football game was played on [[1869 Princeton vs. Rutgers football game|November 6, 1869]], between [[Rutgers Scarlet Knights football|Rutgers]] and [[Princeton Tigers football|Princeton]], two college teams. They consisted of 25 players per team and used a round ball that could not be picked up or carried. It could, however, be kicked or batted with the feet, hands, head, or sides, with the objective being to advance it into the opponent's goal. Rutgers won the game 6–4.<ref name="Rutgers">{{cite web|url=http://scarletknights.com/football/history/first-game.asp|title=Rutgers – The Birthplace of Intercollegiate Football|publisher=[[Rutgers University]]|access-date=November 24, 2012|archive-url=https://web.archive.org/web/20140924154500/http://www.scarletknights.com/football/history/first-game.asp|archive-date=September 24, 2014}}</ref><ref name="No Christian End">{{cite web|title=No Christian End! The Beginnings of Football in America|publisher=[[Professional Football Researchers Association]]|url=http://www.profootballresearchers.com/articles/No_Christian_End.pdf|access-date=November 24, 2012|archive-url=https://web.archive.org/web/20150402124846/http://www.profootballresearchers.com/articles/No_Christian_End.pdf|archive-date=April 2, 2015|url-status=live}}</ref> Collegiate play continued for several years with matches played using the rules of the host school. Representatives of Yale, [[Columbia University|Columbia]], Princeton and Rutgers met on October 19, 1873, to create a standard set of rules for use by all schools. Teams were set at 20 players each, and fields of {{convert|400|x|250|ft|m}} were specified. Harvard abstained from the conference, as they favored a rugby-style game that allowed running with the ball.<ref name="No Christian End" /> After playing [[McGill University]] using both American (known as "the [[Boston game]]") for the first game and Canadian (rugby) rules for the second one,<ref name="No Christian End"/><ref name=bostonpost>[https://www.newspapers.com/clip/2090813/boston-post/ "Foot Ball"], clipping from ''The Boston Post'', May 16, 1874, p. 3</ref> the Harvard players preferred the Canadian style of having only 11 men on the field, running the ball without having to be chased by an opponent, the forward pass, tackling, and using an oblong instead of a round ball.<ref>{{Cite web | url=http://www.rcinet.ca/en/2015/05/14/history-may-14-1874-how-canada-created-american-football/ | title=History- May 14, 1874 How Canada created American football |website=rcinet.ca | date=May 14, 2015 | access-date=October 8, 2018 | archive-url=https://web.archive.org/web/20181009052657/http://www.rcinet.ca/en/2015/05/14/history-may-14-1874-how-canada-created-american-football/ | archive-date=October 9, 2018 | url-status=live | df=mdy-all }}</ref><ref>{{Cite web | url=https://www.mcgill.ca/channels/news/date-history-first-football-game-was-may-14-1874-106694 | title=This Date in History: First football game was May 14, 1874 | access-date=October 8, 2018 |website=mcgill.ca | archive-url=https://web.archive.org/web/20180629074259/https://www.mcgill.ca/channels/news/date-history-first-football-game-was-may-14-1874-106694 | archive-date=June 29, 2018 | url-status=live | df=mdy-all }}</ref>

An 1875 Harvard–Yale game played under rugby-style rules was observed by two Princeton athletes who were impressed by it. They introduced the sport to Princeton, a feat the [[Professional Football Researchers Association]] compared to "selling [[refrigerator]]s to [[Eskimo]]s".<ref name="No Christian End" /> Princeton, Harvard, Yale, and Columbia then agreed to intercollegiate play using a form of [[rugby union]] rules with a modified scoring system.<ref name="Camp and His Followers" /> These schools formed the [[Intercollegiate Football Association]], although Yale did not join until 1879. Yale player [[Walter Camp]], now regarded as the "Father of American Football",<ref name="Camp and His Followers" /><ref name="NFL1869" /> secured rule changes in 1880 that reduced the size of each team from 15 to 11 players and instituted the [[snap (gridiron football)|snap]] to replace the chaotic and inconsistent [[scrum (rugby)|scrum]].<ref name="Camp and His Followers"/> While the game between Rutgers and Princeton is commonly considered the first American football game, several years prior in 1862, the [[Oneida Football Club]] formed as the oldest known football club in the United States. The team consisted of graduates of Boston's elite preparatory schools and played from 1862 to 1865.<ref>[https://www.bostonglobe.com/sports/2012/11/21/oneida-football-club-first-team-play-high-school-football/OBtaKz79JZcmtxkm5WQ40M/story.html "Remembering the first high school football games"] on ''[[The Boston Globe]]'', November 21, 2012</ref>

===Evolution of the game===
[[File:Walter Camp - Project Gutenberg eText 18048.jpg|thumb|upright=1|alt=Walter Camp standing by the railing on a bridge|[[Walter Camp]], the "Father of American Football", in 1878 when Camp was captain of [[Yale Bulldogs football|Yale University's football team]]]]
[[File:WCMorris Spokesman-Review cartoons 099 (1).jpg|thumb|upright=1|alt=Cartoon showing a figure with a skeletal head holding a football upright with extended arms while lying down on a football field|The dangers associated with the sport depicted in a 1908 cartoon by [[William Charles Morris]]]]
The introduction of the snap resulted in an unexpected consequence. Before the snap, the strategy had been to punt if a scrum resulted in bad field position. However, a group of Princeton players realized that, as the snap was uncontested, they could now hold the ball indefinitely to prevent their opponent from scoring. In 1881, in a game between Yale and Princeton, both teams used this strategy to maintain their undefeated records. Each team held the ball, gaining no ground, for an entire half, resulting in a 0–0 tie. This "block game" proved extremely unpopular with both teams' spectators and fans.<ref name="Camp and His Followers" />

A rule change was necessary to prevent this strategy from taking hold, and a reversion to the scrum was considered. However, Camp successfully proposed a rule in 1882 that limited each team to three [[down (gridiron football)|downs]], or tackles, to advance the ball {{convert|5|yd}}. Failure to advance the ball the required distance within those three downs would result in control of the ball being forfeited to the other team. This change effectively made American football a separate sport from rugby, and the resulting five-yard lines added to the field to measure distances made it resemble a [[gridiron (cooking)|gridiron]] in appearance. Other major rule changes included a reduction of the field size to {{convert|110|x|53+1/3|yd|m}} and the adoption of a scoring system that awarded four points for a touchdown, two for a safety and a [[Conversion (gridiron football)|goal following a touchdown]], and five for a [[Field goal|goal from the field]]. Additionally, tackling below the waist was legalized,<ref name="Camp and His Followers">{{cite web|url=http://www.profootballresearchers.com/articles/Camp_And_Followers.pdf|title=Camp and His Followers|publisher=[[Professional Football Researchers Association]]|access-date=November 24, 2012|archive-url=https://web.archive.org/web/20150118174334/http://profootballresearchers.com/articles/Camp_And_Followers.pdf|archive-date=January 18, 2015|url-status=live}}</ref> and a static [[line of scrimmage]] was instituted.<ref>{{cite web |url=http://www.newenglandhistoricalsociety.com/walter-camp-and-birth-modern-football/ |title=Walter Camp and the Birth of Modern Football |date=November 28, 2013 |publisher=New England Historical Society |access-date=January 3, 2019 |quote=As a senior at Yale, Camp prevailed at Massasoit House and cut the number of players to 11 from 15. That year [1882] he also came up with the idea for a static line of scrimmage. |archive-url=https://web.archive.org/web/20181026064524/http://www.newenglandhistoricalsociety.com/walter-camp-and-birth-modern-football/ |archive-date=October 26, 2018 |url-status=live  }}</ref>

Despite these new rules, football remained a violent sport. Dangerous mass-formations like the [[flying wedge]] resulted in serious injuries and deaths.<ref>Bennett (1976), p. 20.</ref> A 1905 peak of 19 fatalities nationwide resulted in a threat by President [[Theodore Roosevelt]] to abolish the game unless major changes were made.<ref>{{cite journal |last=Lewis |first=Guy M. |year=1969 |title=Teddy Roosevelt's Role in the 1905 Football Controversy |journal=The Research Quarterly |volume=40 |pages=717–724 }}</ref> In response, 62 colleges and universities met in New York City to discuss rule changes on December 28, 1905. These proceedings resulted in the formation of the Intercollegiate Athletic Association of the United States, later renamed the [[National Collegiate Athletic Association]] (NCAA).<ref name=NCAA>{{cite web|title=The History of the NCAA|publisher=[[National Collegiate Athletic Association]]|url=https://www.ncaa.org/about/history.html|access-date=November 24, 2012|archive-url =https://web.archive.org/web/20070430205324/http://www.ncaa.org/about/history.html|archive-date=April 30, 2007}}</ref>

The legal [[forward pass]] was introduced in 1906, although its effect was initially minimal due to the restrictions placed on its use. The idea of a 40-yard-wider field was opposed by Harvard due to the size of the new [[Harvard Stadium#Influence on American Football|Harvard Stadium]].<ref>{{cite news|url=https://www.nytimes.com/2007/09/22/sports/ncaafootball/22harvard.html|title=Saturday Night Lights: Harvard Stadium Joins the 21st Century|newspaper=New York Times|date=September 22, 2007 |access-date=April 12, 2016|archive-date=May 29, 2018|archive-url=https://web.archive.org/web/20180529054239/https://www.nytimes.com/2007/09/22/sports/ncaafootball/22harvard.html|url-status=live}}</ref> Other rule changes introduced that year included the reduction of playing time from 70 to 60 minutes and an increase of the distance required for a first down from {{convert|5|to|10|yd|m}}. To reduce infighting and dirty play between teams, the [[Neutral zone (gridiron football)|neutral zone]] was created along the width of the football before the snap.<ref name="Blondy Wallace and the Biggest Football Scandal Ever: 1906">{{cite journal|archive-url=https://web.archive.org/web/20140928221224/http://www.profootballresearchers.org/Coffin_Corner/06-An-209.pdf|archive-date=September 28, 2014|url=http://www.profootballresearchers.org/Coffin_Corner/06-An-209.pdf|title=Blondy Wallace and the Biggest Football Scandal Ever: 1906|last1=Braunwart|first1=Bob|last2=Carroll|first2=Bob|journal=[[The Coffin Corner]]|access-date=November 25, 2012}}</ref> Scoring was also adjusted: points awarded for field goals were reduced to three in 1909<ref name=NFL1869>{{cite web|title=NFL History 1869–1910|website=[[NFL.com]] |archive-url=https://web.archive.org/web/20080102045951/http://www.nfl.com/history/chronology/1869-1910#1892 |archive-date=January 2, 2008 |access-date=November 24, 2012 |url=http://www.nfl.com/history/chronology/1869-1910#1892 |url-status=live }}</ref> and points for touchdowns were raised to six in 1912.<ref name=NFL1911>{{cite web|title=NFL History 1911–1920 |website=[[NFL.com]] |archive-url=https://web.archive.org/web/20080115043331/http://www.nfl.com/history/chronology/1911-1920#1920 |archive-date=January 15, 2008 |access-date=November 24, 2012 |url=http://www.nfl.com/history/chronology/1911-1920#1920 |url-status=live  }}</ref> Also in 1912, the field was shortened to {{convert|100|yd|m}} long, two {{convert|10|yd|m|adj=mid|-long}} end zones were created, and teams were given four downs instead of three to advance the ball {{convert|10|yd|m}}.<ref>{{cite news|url=https://www.newspapers.com/clip/5609757/the_tennessean/|author=Spick Hall|page=19|access-date=June 17, 2016|via=[[Newspapers.com]]|work=The Tennessean|date=September 15, 1912|title=Commodores Face The Hardest Schedule For Many Long Years|archive-date=August 13, 2016|archive-url=https://web.archive.org/web/20160813031423/https://www.newspapers.com/clip/5609757/the_tennessean/|url-status=live}} {{Open access}}</ref><ref name="Danzig1956">{{cite book|title=The History of American Football: Its Great Teams, Players, and Coaches|url=https://archive.org/details/historyofamerica00danz|url-access=registration|last=Danzig |first=Allison |year=1956 |publisher=[[Prentice Hall]] |location=Englewood Cliffs, N.J. |pages=[https://archive.org/details/historyofamerica00danz/page/70 70–71]}}</ref> The [[roughing the passer]] penalty was implemented in 1914, and eligible players were first allowed to catch the ball anywhere on the field in 1918.<ref>Vancil (2000), p. 22.</ref>

===Professional era===
[[File:Pudge heffelfinger.jpg|thumb|upright=0.75|alt=Photo of William Heffelfinger|[[Pudge Heffelfinger]], widely regarded as the first professional football player]]

On November 12, 1892, [[Pudge Heffelfinger]] was paid $500 ({{Inflation|US|500|1892|fmt=eq}}) to play a game for the [[Allegheny Athletic Association]] in a match against the [[Pittsburgh Athletic Club (football)|Pittsburgh Athletic Club]]. This is the first recorded instance of a player being [[Professional football (gridiron)|paid to participate in a game of American football]], although many athletic clubs in the 1880s offered indirect benefits, such as helping players attain employment, giving out trophies or watches that players could pawn for money, or paying double in expense money. Despite these extra benefits, the game had a strict sense of amateurism at the time, and direct payment to players was frowned upon, if not prohibited outright.<ref name=birth>{{cite web|title=The Birth of Pro Football |publisher=[[Pro Football Hall of Fame]] |url=http://www.profootballhof.com/history/general/birth.jsp |access-date=March 19, 2013 |url-status=dead |archive-url=https://web.archive.org/web/20061116215456/http://www.profootballhof.com/history/general/birth.jsp |archive-date=November 16, 2006 }}</ref>

Over time, [[professional football (gridiron)|professional play]] became increasingly common, and with it came rising salaries and unpredictable player movement, as well as the illegal payment of college players who were still in school. The [[National Football League]] (NFL), a group of professional teams that was originally established in 1920 as the American Professional Football Association, aimed to solve these problems. This new league's stated goals included an end to bidding wars over players, prevention of the use of college players, and abolition of the practice of paying players to leave another team.<ref name="The First 25 Years">{{cite journal|last=Clary|first=Jack|year=1994|title=The First 25 Years|journal=[[The Coffin Corner]]|volume=16|issue=4|pages=1, 4–5|url=http://www.profootballresearchers.org/Coffin_Corner/16-04-570.pdf|archive-url=https://web.archive.org/web/20140928221312/http://www.profootballresearchers.org/Coffin_Corner/16-04-570.pdf|archive-date=September 28, 2014}}</ref> By 1922, the NFL had established itself as America's premier professional football league.<ref>Jozsa (2004), pp. 270.</ref>

The dominant form of football at the time was played at the [[college football|collegiate level]]. The upstart NFL received a boost to its legitimacy in 1925, however, when an NFL team, the [[Pottsville Maroons]], defeated a team of [[Notre Dame Fighting Irish football|Notre Dame]] all-stars in an [[1925 NFL Championship controversy#Background|exhibition game]].<ref name="The Curse">{{cite web|url=http://www.phoenixnewtimes.com/2007-01-11/news/the-curse/full|title=The Curse|last=Nelson|first=Robert|date=January 11, 2007|work=[[Phoenix New Times]]|access-date=January 30, 2013|archive-url=https://web.archive.org/web/20131019055036/http://www.phoenixnewtimes.com/2007-01-11/news/the-curse/full|archive-date=October 19, 2013|url-status=live}}</ref> A greater emphasis on the passing game helped professional football to distinguish itself further from the college game during the late 1930s.<ref name="The First 25 Years" /> Football, in general, became increasingly popular following the [[1958 NFL Championship game]], a match between the [[Baltimore Colts]] and the [[New York Giants]] that is still referred to as the "Greatest Game Ever Played". The game, a 23–17 overtime victory by the Colts, was seen by millions of television viewers and had a major influence on the popularity of the sport. This, along with the innovations introduced by the new [[American Football League]] (AFL) in the early 1960s, helped football to become the most popular sport in the United States by the mid-1960s.<ref name="Greatest game ever played">{{cite web|url=http://www.profootballhof.com/history/release.aspx?release_id=1805|title=Greatest game ever played|publisher=[[Pro Football Hall of Fame]]|access-date=March 20, 2013|archive-url=https://web.archive.org/web/20130515154221/http://www.profootballhof.com/history/release.aspx?release_id=1805|archive-date=May 15, 2013|url-status=live}}</ref>

The rival AFL arose in 1960 and challenged the NFL's dominance. The AFL began in relative obscurity but eventually thrived, with an initial television contract with the [[American Broadcasting Company|ABC]] television network. The AFL's existence forced the conservative NFL to expand to Dallas and Minnesota in an attempt to destroy the new league. Meanwhile, the AFL introduced many new features to professional football in the United States: official time was kept on a scoreboard clock rather than on a watch in the referee's pocket, as the NFL did; optional two-point conversions by pass or run after touchdowns; names on the jerseys of players; and several others, including expansion of the role of minority players, actively recruited by the league in contrast to the NFL. The AFL also signed several star college players who had also been drafted by NFL teams. Competition for players heated up in 1965, when the AFL [[New York Jets]] signed rookie [[Joe Namath]] to a then-record $437,000 contract (equivalent to ${{formatprice|{{inflation|US-GDP|437000|1965}}}} in {{inflation-year|US-GDP}}{{inflation-fn|US-GDP}}). A five-year, $40&nbsp;million <!-- This currency conversion produces a madly overinflated amount in total contradiction to the previous conversion which is for the same year... (equivalent to ${{formatprice|{{inflation|US-GDP|400000000|1965}}}} in {{inflation-year|US-GDP}}{{inflation-fn|US-GDP}})--> [[NBC]] television contract followed, which helped to sustain the young league. The bidding war for players ended in 1966 when NFL owners approached the AFL regarding a merger, and the two leagues [[AFL–NFL merger|agreed on one]] that took full effect in 1970. This agreement provided for a common draft that would take place each year, and it instituted an annual World Championship game to be played between the champions of each league. This championship game began play at the end of the 1966 season. Once the merger was completed, it was no longer a championship game between two leagues and reverted to the NFL championship game, which came to be known as the [[Super Bowl]].<ref name="The Second 25 Years">{{cite journal|last=Clary|first=Jack|year=1994|title=The Second 25 Years|journal=[[The Coffin Corner]]|volume=16|issue=5|pages=4–5|url=http://www.profootballresearchers.org/Coffin_Corner/16-05-575.pdf|archive-url=https://web.archive.org/web/20141019125833/http://www.profootballresearchers.org/Coffin_Corner/16-05-575.pdf|archive-date=October 19, 2014}}</ref>

College football maintained a tradition of postseason [[bowl games]]. Each bowl game was associated with a particular conference and earning a spot in a bowl game was the reward for winning a conference. This arrangement was profitable, but it tended to prevent the two top-ranked teams from meeting in a true national championship game, as they would normally be committed to the bowl games of their respective conferences. Several systems have been used since 1992 to determine a national champion of college football. The first was the [[Bowl Coalition]], in place from 1992 to 1994. This was replaced in 1995 by the [[Bowl Alliance]], which gave way in 1997 to the [[Bowl Championship Series]] (BCS).<ref name=BCS>{{cite web | title = BCS Chronology |publisher=FOX Sports on MSN| year = 2006 | url = http://www.bcsfootball.org/bcsfb/history | website=bcsfootball.org | access-date =March 19, 2013|archive-url=https://web.archive.org/web/20100113132437/http://www.bcsfootball.org/bcsfb/history|archive-date=January 13, 2010|url-status=dead}}</ref> The BCS arrangement [[BCS controversies|proved to be controversial]], and was replaced in 2014 by the [[College Football Playoff]] (CFP).<ref name="Presidents get playoff plan right">{{cite web|url=http://espn.go.com/college-football/story/_/id/8099205/college-football-time-celebrate-approval-four-team-playoff|title=Presidents get playoff plan right|author=Wojciechowski, Jean|date=June 26, 2012|work=[[ESPN.com]]|access-date=March 20, 2013|archive-url=https://web.archive.org/web/20130523003316/http://espn.go.com/college-football/story/_/id/8099205/college-football-time-celebrate-approval-four-team-playoff|archive-date=May 23, 2013|url-status=live|author-link=Gene Wojciechowski}}</ref><ref>{{cite web|first1=Ralph D.|last1=Russo|title=NCAA College Football Playoff pits powerhouses Ohio State and Oregon|url=https://www.thestar.com/sports/football/2015/01/02/ncaa_college_football_playoff_pits_powerhouses_ohio_state_and_oregon.html|work=[[Toronto Star]]|access-date=January 16, 2015|date=January 2, 2015|archive-url=https://web.archive.org/web/20150106094442/http://www.thestar.com/sports/football/2015/01/02/ncaa_college_football_playoff_pits_powerhouses_ohio_state_and_oregon.html|archive-date=January 6, 2015|url-status=live}}</ref>

==Teams and positions==
{{Main|American football positions}}
[[File:43BaseDefense.svg|thumb|left|upright=1|alt=Diagram showing a green background with a white horizontal line dividing it into two-halves, with eleven small blue squares representing defense players in a formation above the line, and eleven small red circles representing offense players in another formation below the line, with two text captions "Defense" and "Offense", the former placed above the line and the latter below the line|A diagram of a typical pre-snap formation. The offense (red) is lined up in a variation of the [[I formation]], while the defense (blue) is lined up in the [[4–3 defense]]. Both formations are legal.]]

A football game is played between two teams of 11 players each.<ref name="NFL Rules 2012, p. 21">NFL Rules 2012, p.&nbsp;21.</ref><ref name="NCAA Rules 2011–2012, p. 15" /><ref name="NFHS Rules 2012, p. 11">NFHS Rules 2012, p.&nbsp;11.</ref> Playing with more on the field is punishable by a penalty.<ref name="NFL Rules 2012, p. 21" /><ref name="NCAA Rules 2011–2012, p. 107">NCAA Rules 2011–2012, p.&nbsp;107.</ref><ref name="NFHS Rules 2012, pp. 71-72">NFHS Rules 2012, pp.&nbsp;71–72.</ref> Teams may substitute [[Free substitution|any number of their players]] between downs;<ref name="NFL Rules 2012, pp. 21-22">NFL Rules 2012, pp.&nbsp;21–22.</ref><ref name="NCAA Rules 2011–2012, pp. 53-54">NCAA Rules 2011–2012, pp.&nbsp;53–54.</ref><ref name="NFHS Rules 2012, pp. 45-46">NFHS Rules 2012, pp.&nbsp;45–46.</ref> this "platoon" system replaced the original system, which featured limited substitution rules, and has resulted in teams utilizing specialized offensive, defensive and [[American football positions#Special teams|special teams]] units.<ref name="The innovator">{{cite web|url=http://michigantoday.umich.edu/2010/07/story.php?id=7795|title=The innovator|last=Dickson|first=James David|date=July 14, 2010|publisher=[[Michigan Today]]|access-date=October 7, 2012|archive-url=https://web.archive.org/web/20131019065323/http://michigantoday.umich.edu/2010/07/story.php?id=7795|archive-date=October 19, 2013}}</ref> The number of players allowed on an active roster varies by league; the NFL has a 53-man roster,<ref name="The Anatomy of a 53-Man Roster in the NFL">{{cite web |last1=Lillibridge |first1=Marc |title=The Anatomy of a 53-Man Roster in the NFL |url=https://bleacherreport.com/articles/1640782-the-anatomy-of-a-53-man-roster-in-the-nfl |website=Bleacher Report |access-date=January 25, 2024 |language=en |date=May 16, 2023}}</ref> while NCAA Division I allows teams to have 63 scholarship players in the FCS and 85 scholarship players in the FBS, respectively.<ref name="NCAA votes to eliminate annual initial counter limits">{{cite web |last1=Staff |first1=Max Olson |title=NCAA votes to eliminate annual initial counter limits |url=https://theathletic.com/4930190/2023/10/04/college-football-initial-counter-rules-eliminated/ |website=[[The Athletic]] |access-date=January 25, 2024 |language=en |date=October 4, 2023}}</ref> 

Individual players in a football game must be designated with a [[Uniform number (American football)|uniform number]] between 1 and 99, though some teams may [[Retired number|"retire" certain numbers]], making them unavailable to players. NFL teams are required to number their players by a league-approved numbering system, and any exceptions must be approved by the [[Commissioner#Sports|commissioner]].<ref name="NFL Rules 2012, p. 21" /> NCAA and NFHS teams are "strongly advised" to number their offensive players according to a league-suggested numbering scheme.<ref name="NCAA Rules 2011–2012, pp. 21-22">NCAA Rules 2011–2012, pp.&nbsp;21–22.</ref><ref name="NFHS Rules 2012, pp. 16-17">NFHS Rules 2012, pp.&nbsp;16–17.</ref>

Although the sport is played almost exclusively by men, women are [[List of female American football players|eligible to play]] in high school, college, and professional football. No woman has ever played in the NFL, but women have played in high school and college football games.<ref name="For women, tackling NFL is a long shot">{{cite web |last1=McManus |first1=Jane |title=For women, tackling NFL is a long shot |url=http://www.espn.com/espnw/news/article/6516042/women-pros-women-tackling-nfl-long-shot |publisher=[[ESPN.com#ESPNW|ESPNW]] |access-date=August 10, 2019 |date=May 11, 2011 |archive-date=August 10, 2019 |archive-url=https://web.archive.org/web/20190810151900/http://www.espn.com/espnw/news/article/6516042/women-pros-women-tackling-nfl-long-shot |url-status=live }}</ref> In 2018, 1,100 of the 225,000 players in [[Pop Warner Little Scholars]] youth football were girls, and around 11% of the 5.5&nbsp;million Americans who report playing tackle football are female according to the Sports and Fitness Industry Association.<ref name="More Girls Are Playing Football">{{cite web |last1=de la Cretaz |first1=Britni |title=More Girls Are Playing Football. Is That Progress? |url=https://www.nytimes.com/2018/02/02/well/family/football-girls-concussions.html |work=[[The New York Times]] |access-date=August 10, 2019 |date=February 2, 2018 |archive-date=August 10, 2019 |archive-url=https://web.archive.org/web/20190810152446/https://www.nytimes.com/2018/02/02/well/family/football-girls-concussions.html |url-status=live }}</ref>

===Offensive unit===
[[File:Hurricanes Quarterback.JPG|thumb|upright=1|A quarterback for the [[Kiel Baltic Hurricanes]] under center, ready to take the snap]]
The role of the offensive unit is to advance the football down the field with the ultimate goal of scoring a [[touchdown]].<ref name="NFL in a nutshell">{{cite news|url=http://news.bbc.co.uk/sport2/hi/other_sports/american_football/3192002.stm|title=NFL in a nutshell|date=October 19, 2005|work=BBC Sport|access-date=November 20, 2012|archive-url=https://web.archive.org/web/20121122215916/http://news.bbc.co.uk/sport2/hi/other_sports/american_football/3192002.stm|archive-date=November 22, 2012|url-status=live}}</ref>

The offensive team must line up in a legal [[Formation (American football)|formation]] before they can snap the ball. An offensive formation is considered illegal if there are more than four players in the [[Glossary of American football#backfield|backfield]] or fewer than five players numbered 50–79 on the offensive line.<ref name="NCAA Rules 2011–2012, p. 15">NCAA Rules 2011–2012, p.&nbsp;15.</ref><ref name="NFL Rules 2012, pp. 21-24">NFL Rules 2012, pp.&nbsp;21–24.</ref><ref name="NFHS Rules 2012, pp. 57-58">NFHS Rules 2012, pp.&nbsp;57–58.</ref> Players can line up temporarily in a position whose eligibility is different from what their number permits as long as they report the change immediately to the referee, who then informs the defensive team of the change.<ref name="NFL Rules 2012, pp. 36, 40">NFL Rules 2012, pp.&nbsp;36, 40.</ref> Neither team's players, except the [[Center (gridiron football)|center]] (C), are allowed to line up in or cross the neutral zone until the ball is snapped. Interior offensive linemen are not allowed to move until the snap of the ball.<ref name="Common Penalties in American Football">{{cite web|url=http://www.dummies.com/how-to/content/common-penalties-in-american-football.html|title=Common Penalties in American Football|last1=Long|first1=Howie|last2=Czarnecki|first2=John|author-link1=Howie Long|publisher=[[For Dummies|Dummies.com]]|access-date=November 23, 2012|archive-url=https://web.archive.org/web/20121223110721/http://www.dummies.com/how-to/content/common-penalties-in-american-football.html|archive-date=December 23, 2012|url-status=live}}</ref>

The main backfield positions are the [[quarterback]] (QB), [[Halfback (American football)|halfback/tailback]] (HB/TB), and [[fullback (gridiron football)|fullback]] (FB). The quarterback is the leader of the offense. Either the quarterback or a coach calls the plays. Quarterbacks typically inform the rest of the offense of the play in the [[Huddle#American football|huddle]] before the team lines up. The quarterback lines up behind the center to take the snap and then hands the ball off, throws it, or runs with it.<ref name="NFL in a nutshell" />

The primary role of the halfback, also known as the [[running back]] or tailback, is to carry the ball on running plays. Halfbacks may also serve as receivers. Fullbacks tend to be larger than halfbacks and function primarily as blockers, but they are sometimes used as runners in short-yardage or goal-line situations.<ref name="Football Players' Roles in Team Offense and Defense">{{cite web|url=http://www.dummies.com/how-to/content/football-players-roles-in-team-offense-and-defense.html|title=Football Players' Roles in Team Offense and Defense|publisher=[[For Dummies|Dummies.com]]|access-date=January 14, 2013|archive-url=https://web.archive.org/web/20130106181746/http://www.dummies.com/how-to/content/football-players-roles-in-team-offense-and-defense.html|archive-date=January 6, 2013|url-status=live}}</ref> They are seldom used as receivers.<ref name="Fullbacks back en vogue">{{cite web|url=http://sports.espn.go.com/nfl/columns/story?columnist=pasquarelli_len&id=5238185|title=Fullbacks back en vogue|last=Pasquarelli|first=Len|date=June 1, 2010|work=[[ESPN.com]]|access-date=November 22, 2012|archive-url=https://web.archive.org/web/20140725082524/http://sports.espn.go.com/nfl/columns/story?columnist=pasquarelli_len&id=5238185|archive-date=July 25, 2014|url-status=live}}</ref>

The [[Lineman (gridiron football)#offensive line|offensive line]] (OL) consists of several players whose primary function is to [[Blocking (American football)|block]] members of the defensive line from tackling the ball carrier on running plays or [[Quarterback sack|sacking]] the quarterback on passing plays.<ref name="Football Players' Roles in Team Offense and Defense" /> The leader of the offensive line is the center, who is responsible for snapping the ball to the quarterback, blocking,<ref name="Football Players' Roles in Team Offense and Defense" /> and for making sure that the other linemen do their jobs during the play.<ref name="Centers: The Unsung Heroes of Football">{{cite web|url=http://www.active.com/football/Articles/Centers-The-Unsung-Heroes-of-Football|title=Centers: The Unsung Heroes of Football|last=Wood|first=Ryan|publisher=Active.com|access-date=November 22, 2012|date=October 23, 2009|archive-url=https://web.archive.org/web/20130530052506/http://www.active.com/football/Articles/Centers-The-Unsung-Heroes-of-Football|archive-date=May 30, 2013|url-status=live}}</ref> On either side of the center are the [[Guard (gridiron football)|guards]] (G), while [[Tackle (gridiron football position)|tackles]] (T) line up outside the guards.

The principal receivers are the [[wide receiver]]s (WR) and the [[tight end]]s (TE).<ref name="Football's Offensive Team: The Receivers">{{cite web|url=http://www.dummies.com/how-to/content/footballs-offensive-team-the-receivers.html|title=Football's Offensive Team: The Receivers|last1=Long|first1=Howie|last2=Czarnecki|first2=John|author-link1=Howie Long|publisher=[[For Dummies|Dummies.com]]|access-date=November 22, 2012|archive-url=https://web.archive.org/web/20130303005856/http://www.dummies.com/how-to/content/footballs-offensive-team-the-receivers.html|archive-date=March 3, 2013|url-status=live}}</ref> Wide receivers line up on or near the line of scrimmage, split outside the line. The main goal of the wide receiver is to catch passes thrown by the quarterback,<ref name="Football Players' Roles in Team Offense and Defense" /> but they may also function as decoys or as blockers during running plays. Tight ends line up outside the tackles and function both as receivers and as blockers.<ref name="Football Players' Roles in Team Offense and Defense" />

===Defensive unit===
[[File:Arian Foster fumble.jpg|thumb|upright=1|alt=Photograph of defensive players tackling an offensive player who has just lost control of the football | [[Dallas Cowboys]] defensive players force [[Houston Texans]] running back [[Arian Foster]] to fumble the ball.]]
The role of the defense is to prevent the offense from scoring by [[Tackle (football move)#American and Canadian football|tackling]] the ball carrier or by forcing [[Turnover (gridiron football)|turnovers]] ([[interception]]s or [[fumble]]s).<ref name="NFL in a nutshell" />

The [[defensive line]] (DL) consists of [[defensive end]]s (DE) and [[defensive tackle]]s (DT). Defensive ends line up on the ends of the line, while defensive tackles line up inside, between the defensive ends. The primary responsibilities of defensive ends and defensive tackles are to stop running plays on the outside and inside, respectively, to pressure the quarterback on passing plays, and to occupy the line so that the [[linebacker]]s can break through.<ref name="Football Players' Roles in Team Offense and Defense" />

Linebackers line up behind the defensive line but in front of the defensive backfield. They are divided into two types: middle linebackers (MLB) and outside linebackers (OLB). Linebackers tend to serve as the defensive leaders and call the defensive plays, given their vantage point of the offensive backfield. Their roles include defending the run, pressuring the quarterback, and tackling backs, wide receivers, and tight ends in the passing game.<ref name="Football's Defensive Team: The Linebackers">{{cite web|url=http://www.dummies.com/how-to/content/footballs-defense-team-the-linebackers.html|title=Football's Defensive Team: The Linebackers|last1=Long|first1=Howie|last2=Czarnecki|first2=John|author-link1=Howie Long|publisher=[[For Dummies|Dummies.com]]|access-date=November 23, 2012|archive-url=https://web.archive.org/web/20130122084614/http://www.dummies.com/how-to/content/footballs-defense-team-the-linebackers.html|archive-date=January 22, 2013|url-status=live}}</ref>

The [[defensive back]]field, often called the secondary, consists of [[cornerback]]s (CB) and [[Safety (gridiron football position)|safeties]] (S). Safeties are themselves divided into free safeties (FS) and strong safeties (SS).<ref name="Football Players' Roles in Team Offense and Defense" /> Cornerbacks line up outside the defensive formation, typically opposite a receiver to be able to cover them. Safeties line up between the cornerbacks but farther back in the secondary. Safeties tend to be viewed as "the last line of defense" and are responsible for stopping deep passing plays as well as breakout running plays.<ref name="Football Players' Roles in Team Offense and Defense" />
{{-}}

===Special teams unit===
[[File:Jeff Reed kickoff 2006.jpg|thumb|upright=1|alt=Four players run up the field as the kicker executes a kickoff | Kicker [[Jeff Reed (American football)|Jeff Reed]] of the [[Pittsburgh Steelers]] executes a kickoff.]]
The special teams unit is responsible for all kicking plays. The special teams unit of the team in control of the ball tries to execute field goal (FG) attempts, [[Punt (gridiron football)|punts]], and [[Kickoff (gridiron football)|kickoffs]], while the opposing team's unit will aim to block or return them.<ref name="NFL in a nutshell" />

Three positions are specific to the field goal and PAT (point-after-touchdown) unit: the [[placekicker]] (K or PK), [[Holder (American football)|holder]] (H), and [[long snapper]] (LS). The long snapper's job is to snap the football to the holder, who will catch and position it for the placekicker. There is not usually a holder on kickoffs, because the ball is kicked off a tee; however, a holder may be used in certain situations, such as if wind is preventing the ball from remaining upright on the tee. The player on the receiving team who catches the ball is known as the [[kickoff returner]] (KR).<ref name="The Role of Special Teams in a Football Game">{{cite web|url=http://www.dummies.com/how-to/content/the-role-of-special-teams-in-a-football-game.html|title=The Role of Special Teams in a Football Game|last1=Long|first1=Howie|last2=Czarnecki|first2=John|author-link1=Howie Long|publisher=[[For Dummies|Dummies.com]]|access-date=January 12, 2012|archive-url=https://web.archive.org/web/20120124014652/http://www.dummies.com/how-to/content/the-role-of-special-teams-in-a-football-game.html|archive-date=January 24, 2012|url-status=live}}</ref>

The positions specific to punt plays are the [[punter (football)|punter]] (P), long snapper, [[upback]], and [[Gunner (American football)|gunner]]. The long snapper snaps the football directly to the punter, who then drops and kicks it before it hits the ground. Gunners line up split outside the line and race down the field, aiming to tackle the [[punt returner]] (PR)—the player who catches the punt. Upbacks line up a short distance behind the line of scrimmage, providing additional protection to the punter.<ref name="Football Special Teams: Players on a Punt Team">{{cite web|url=http://www.dummies.com/how-to/content/football-special-teams-players-on-a-punt-team.html|title=Football Special Teams: Players on a Punt Team|last1=Long|first1=Howie|last2=Czarnecki|first2=John|author-link1=Howie Long|publisher=[[For Dummies|Dummies.com]]|access-date=January 12, 2012|archive-url=https://web.archive.org/web/20120126113938/http://www.dummies.com/how-to/content/football-special-teams-players-on-a-punt-team.html|archive-date=January 26, 2012|url-status=live}}</ref>

==Rules==
{{Main|American football rules}}
===Scoring===
[[File:2006 Navy - Tusla.jpg|thumb|upright=1|alt=A player pursued by an opponent dives into the end zone in front of an official to score a touchdown.|A player for the [[Navy Midshipmen football|Navy Midshipmen]] (dark jersey) scores a touchdown while a defender from the [[Tulsa Golden Hurricane football|Tulsa Golden Hurricane]] (in white) looks on. The goal line is marked by the small orange pylon.]]
In football, the winner is the team that has scored more points at the end of the game. There are multiple ways to score in a football game. The touchdown (TD), worth six points, is the most valuable scoring play in American football. A touchdown is scored when a live ball is advanced into, caught, or recovered in the opposing team's end zone.<ref name="NFL in a nutshell" /> The scoring team then attempts a try, more commonly known as the point(s)-after-touchdown (PAT) or conversion, which is a single scoring opportunity. This is generally attempted from the two- or three-yard line, depending on the level of play. If the PAT is scored by a place kick or drop kick through the goal posts, it is worth one point, typically called the extra point. If the PAT is scored by what would normally be a touchdown, it is worth two points; this is known as a [[two-point conversion]]. In general, the extra point is almost always successful, while the two-point conversion is a much riskier play with a higher probability of failure; accordingly, extra point attempts are far more common than two-point conversion attempts.<ref name="Duke">{{cite journal|last=Sackrowitz|first=Harold|year=2000|title=Refining the Point(s)-After-Touchdown Decision|journal=Department of Statistical Science|volume=13|issue=3|pages=29–30, 33–34|url=http://www.stat.duke.edu/~dalene/chance/chanceweb/133.sackrowitz.pdf|access-date=October 23, 2012|archive-url=https://web.archive.org/web/20131002214621/http://www.stat.duke.edu/~dalene/chance/chanceweb/133.sackrowitz.pdf|archive-date=October 2, 2013|url-status=dead}}</ref>

A field goal (FG), worth three points, is scored when the ball is place kicked or drop kicked through the uprights and over the crossbars of the defense's goalposts.<ref name="NFL Rules 2012, p. 57-59">NFL Rules 2012, pp.&nbsp;57–59.</ref><ref name="NCAA Rules 2011–2012, p. 79-80">NCAA Rules 2011–2012, pp.&nbsp;79–80.</ref><ref name="NFHS Rules 2012, p. 66">NFHS Rules 2012, p.&nbsp;66.</ref> In practice, almost all field goal attempts are done via place kick. While drop kicks were common in the early days of the sport, the shape of modern footballs makes it difficult to reliably drop kick the ball. The last successful scoring play by drop kick in the NFL was accomplished in 2006; prior to that, the last successful drop kick had been made in 1941.<ref>{{cite web |title=The last dropkick |url=https://www.profootballhof.com/news/2015/12/the-last-dropkick/ |website=[[Pro Football Hall of Fame]] |access-date=January 25, 2024 |language=en |date=December 6, 2015}}</ref> After a PAT attempt or successful field goal, the scoring team must kick the ball off to the other team.<ref name="Beginner's Guide to Football">{{cite web|url=http://www.nfl.com/rulebook/beginnersguidetofootball|title=Beginner's Guide to Football|website=[[National Football League]]|access-date=September 30, 2012|archive-url=https://web.archive.org/web/20110216225503/http://www.nfl.com/rulebook/beginnersguidetofootball|archive-date=February 16, 2011|url-status=live}}</ref>

A [[Safety (gridiron football score)|safety]] is scored when the ball carrier is tackled in his own end zone. Safeties are worth two points, which are awarded to the defense.<ref name="NFL in a nutshell" /> In addition, the team that conceded the safety must kick the ball to the scoring team via a [[Safety (gridiron football score)#Resuming play after a safety|free kick]].<ref name="NFL Rules 2012, p. 60">NFL Rules 2012, p.&nbsp;60</ref>

===Field and equipment===
{{Main|American football field}}
[[File:Edward Jones Dome endzone view.jpg|thumb|upright=1|alt= Photograph of a football field taken from the end zone showing goal posts in the foreground | A football field as seen from behind one end zone. The tall, yellow goal posts mark where the ball must pass for a successful field goal or extra point. The large, rectangular area marked with the team name is the end zone.]]
Football games are played on a rectangular [[American football field|field]] that measures {{convert|120|yd|m}} long and {{convert|53+1/3|yd|m}} wide. Lines marked along the ends and sides of the field are known as the end lines and [[sidelines]]. [[Goal line (American football)|Goal lines]] are marked {{convert|10|yd|m}} inward from each end line.<ref name="NFL Rules 2012, p. v, 1">NFL Rules 2012, p.&nbsp;v,&nbsp;1.</ref><ref name="NCAA Rules 2011–2012, pp. 18-19, 23–24">NCAA Rules 2011–2012, pp.&nbsp;18–19, 23–24.</ref><ref name="NFHS Rules 2012, pp. 11-12, 13, 28">NFHS Rules 2012, pp.&nbsp;11–12, 13, 28.</ref>

Weighted pylons are placed the sidelines on the inside corner of the intersections with the goal lines and end lines. White markings on the field identify the distance from the end zone. Inbound lines, or [[hash marks]], are short parallel lines that mark off {{convert|1|yd|m|adj=on}} increments. [[Yard lines]], which can run the width of the field, are marked every {{convert|5|yd|m}}. A one-yard-wide line is placed at each end of the field; this line is marked at the center of the two-yard line in professional play and at the three-yard line in college play. Numerals that display the distance from the closest goal line in yards are placed on both sides of the field every ten yards.<ref name="NFL Rules 2012, p. v, 1"/><ref name="NCAA Rules 2011–2012, pp. 18-19, 23–24"/><ref name="NFHS Rules 2012, pp. 11-12, 13, 28"/>

[[Goalposts]] are located at the center of the plane of the two end lines. The crossbar of these posts is {{convert|10|ft|m}} above the ground, with vertical uprights at the end of the crossbar {{convert|18|ft|6|in|m}} apart for professional and collegiate play, and {{convert|23|ft|4|in|m}} apart for high school play.<ref name="NFL Rules 2012, p. 2" /><ref name="NCAA Rules 2011–2012, p. 18" /><ref name="NFHS Rules 2012, p. 14-15"/> The uprights extend vertically {{convert|35|ft|m}} on professional fields, a minimum of {{convert|10|yd|m}} on college fields, and a minimum of {{convert|10|ft|m}} on high school fields. Goal posts are padded at the base, and orange ribbons are normally placed at the tip of each upright as indicators of wind strength and direction.<ref name="NFL Rules 2012, p. 2">NFL Rules 2012, p.&nbsp; 2.</ref><ref name="NCAA Rules 2011–2012, p. 18">NCAA Rules 2011–2012, p.&nbsp;18.</ref><ref name="NFHS Rules 2012, p. 14-15">NFHS Rules 2012, p.&nbsp;14.</ref>

The [[Ball (gridiron football)|football]] itself is a [[prolate spheroid]] leather ball, similar to the balls used in rugby or [[Australian rules football]].<ref name="Bounce of an oval shaped football">{{cite journal|last=Cross|first=Rod|title=Bounce of an oval shaped football|journal=Sports Technology|date=August 2010|volume=3|issue=3|pages=168–180|doi=10.1080/19346182.2011.564283|s2cid=108409393|url=https://www.researchgate.net/publication/233184599|access-date=April 23, 2014|archive-date=February 15, 2022|archive-url=https://web.archive.org/web/20220215012453/https://www.researchgate.net/publication/233184599_Bounce_of_an_oval_shaped_football|url-status=live}}</ref> To contain the [[compressed air]] within it, a pig's bladder was commonly used before the advent of [[artificial rubber]] inside the leather outer shell to [[pressure vessel|sustain crushing forces]].<ref name="si1">{{cite news |url=https://www.si.com/nfl/2019/01/31/how-cow-becomes-football-horween-wilson |title=How a Cow Becomes a Football |date=January 31, 2019 }}</ref><ref name="pendle">{{cite news |url=https://www.pendlesportswear.co.uk/blog/footballs-a-history/ |title=History of Footballs &#124; the First Football &#124; Pendle Sportswear Blog |date=December 20, 2019 }}</ref> At all levels of play, the football is inflated to {{convert|12+1/2|to|13+1/2|psi}}, or just under one atmosphere, and weighs {{convert|14|to|15|oz|g}};<ref name="NFHS Rules 2012, p. 14-15"/><ref name="NCAA Rules 2011–2012, p. 20">NCAA Rules 2011–2012, p.&nbsp;20.</ref><ref name="NFL Rules 2012, p. 3">NFL Rules 2012, p.&nbsp;3.</ref> beyond that, the exact dimensions vary slightly. In professional play the ball has a long axis of {{convert|11|to|11+1/4|in|cm}}, a long circumference of {{convert|28|to|28+1/2|in|cm}}, and a short circumference of {{convert|21|to|21+1/4|in|cm}}.<ref>{{cite web|url=http://uaasnfl.blob.core.windows.net/live/1807/2015_nfl_rule_book_final.pdf |title=Official Playing Rules of the National Football League |url-status=dead |archive-url=https://web.archive.org/web/20160303235622/http://uaasnfl.blob.core.windows.net/live/1807/2015_nfl_rule_book_final.pdf |archive-date=March 3, 2016 }}, p.3</ref> In college and high school play the ball has a long axis of {{convert|10+7/8|to|11+7/16|in|cm}}, a long circumference of {{convert|27+3/4|to|28+1/2|in|cm}}, and a short circumference of {{convert|20+3/4|to|21+1/4|in|cm}}.<ref name="NFHS Rules 2012, p. 14-15"/><ref name="NCAA Rules 2011–2012, p. 20" />

===Duration and time stoppages===
Football games last for a total of 60 minutes in professional and college play and are divided into two halves of 30 minutes and four quarters of 15 minutes.<ref name="NFL Rules 2012, p. 14">NFL Rules 2012, p.&nbsp;14.</ref><ref name="NCAA Rules 2011–2012, p. 45">NCAA Rules 2011–2012, p.&nbsp;45.</ref> High school football games are 48 minutes in length with two halves of 24 minutes and four quarters of 12 minutes.<ref name="NFHS Rules 2012, pp. 38-39">NFHS Rules 2012, pp.&nbsp;38–39.</ref> The two halves are separated by a [[half-time|halftime]] period, and the first and third quarters are followed by a short break.<ref name="NFL Rules 2012, p. 14" /><ref name="NCAA Rules 2011–2012, p. 45" /><ref name="NFHS Rules 2012, p. 39">NFHS Rules 2012, p.&nbsp;39.</ref> Before the game starts, the referee and each team's [[captain (sports)|captain]] meet at midfield for a [[coin toss]]. The visiting team can call either "heads" or "tails"; the winner of the toss chooses whether to receive or kick off the ball or which goal they wish to defend. They can defer their choice until the second half. Unless the winning team decides to defer, the losing team chooses the option the winning team did not select—to receive, kick, or select a goal to defend to begin the second half. Most teams choose to receive or defer, because choosing to kick the ball to start the game allows the other team to choose which goal to defend.<ref name="TMQ's all-haiku NFL preview">{{cite web|title=TMQ's all-haiku NFL preview|url=http://sports.espn.go.com/espn/page2/story?page=easterbrook/080902|work=[[ESPN.com]]|access-date=October 1, 2013|author=Easterbrook, Gregg|date=September 4, 2008|archive-url=https://web.archive.org/web/20131012030031/http://sports.espn.go.com/espn/page2/story?page=easterbrook%2F080902|archive-date=October 12, 2013|url-status=live|author-link = Gregg Easterbrook}}</ref> Teams switch goals following the first and third quarters.<ref name="How Football Game Time Is Measured in Quarters">{{cite web|url=http://www.dummies.com/how-to/content/how-football-game-time-is-measured-in-quarters.html|title=How Football Game Time Is Measured in Quarters|publisher=[[For Dummies|Dummies.com]]|access-date=December 2, 2012|archive-url=https://web.archive.org/web/20121126053220/http://www.dummies.com/how-to/content/how-football-game-time-is-measured-in-quarters.html|archive-date=November 26, 2012|url-status=live}}</ref> If a down is in progress when a quarter ends, play continues until the down is completed.<ref name="NFL Rules 2012, p. 14-18">NFL Rules 2012, pp.&nbsp;14–18</ref><ref name="NCAA Rules 2011–2012, pp. 47-53">NCAA Rules 2011–2012, pp.&nbsp;47–53.</ref><ref name="NFHS Rules 2012, pp. 38-45">NFHS Rules 2012, pp.&nbsp;38–45</ref> If certain fouls are committed during play while time has expired, the quarter may be extended through an [[untimed play|untimed down]].<ref name="Ask the official: Extra-point ruling and untimed downs">{{cite web |last1=Wire |first1=Adam |title=Ask the official: Extra-point ruling and untimed downs |url=https://blogs.usafootball.com/blog/4611/ask-the-official-extra-point-ruling-and-untimed-downs |website=[[USA Football]] |access-date=January 25, 2024 |date=October 9, 2017}}</ref>

Games last longer than their defined length due to play stoppages—the average NFL game lasts slightly over three hours.<ref name="USA Today">{{cite web|url=http://content.usatoday.com/communities/gameon/post/2011/10/delay-of-game-nfl-games-taking-longer-in-2011-espn-chris-mortensen-dan-masonson/1|title=Delay of game: NFL games running longer in 2011|last=McCarthy|first=Michael|date=October 27, 2011|work=[[USA Today]]|access-date=December 3, 2012|archive-url=https://web.archive.org/web/20130707152325/http://content.usatoday.com/communities/gameon/post/2011/10/delay-of-game-nfl-games-taking-longer-in-2011-espn-chris-mortensen-dan-masonson/1|archive-date=July 7, 2013|url-status=live}}</ref> Time in a football game is measured by the game clock. An operator is responsible for starting, stopping and operating the game clock based on the direction of the appropriate [[Official (American football)|official]].<ref name="NFL Rules 2012, p. 14" /><ref name="NCAA Rules 2011–2012, pp. 16, 41">NCAA Rules 2011–2012, pp.&nbsp;16,&nbsp;41.</ref> A separate [[play clock]] is used to show the amount of time within which the offense must initiate a play. The play clock is set to 25 seconds after certain administrative stoppages in play and to 40 seconds when play is proceeding without such stoppages. If the offense fails to start a play before the play clock reads "00", a [[Delay of game#American|delay of game]] foul is called on the offense.<ref name="NFL Rules 2012, p. 14-18" /><ref name="NCAA Rules 2011–2012, pp. 41, 46–47">NCAA Rules 2011–2012, pp.&nbsp;41,&nbsp;46–47.</ref><ref name="NFHS Rules 2019">NFHS Rules 2019.</ref>

===Advancing the ball and downs===
[[File:Delhomme goes deep.jpg|thumb|upright=1|alt=A quarterback is shown in the process of throwing a forward pass. His offensive linemen are in front of him.|[[Carolina Panthers]] quarterback [[Jake Delhomme]] (number 17) in the motion of throwing a forward pass]]
There are two main ways the offense can advance the ball: [[Rush (gridiron football)|running]] and [[Forward pass#Gridiron football|passing]]. In a typical play, the center passes the ball backwards and between their legs to the quarterback in a process known as the [[Snap (gridiron football)|snap]]. The quarterback then either hands the ball off to a running back, throws the ball, or runs with it. The play ends when the player with the ball is tackled or goes out-of-bounds or a pass hits the ground without a player having caught it. A forward pass can be legally attempted only if the passer is behind the line of scrimmage; only one forward pass can be attempted per down.<ref name="Beginner's Guide to Football" /> As in rugby, players can also [[lateral pass|pass the ball backwards]] at any point during a play.<ref>{{cite web |title=Backward pass |url=http://www.nfl.com/rulebook/backwardpass |website=[[National Football League]] |archive-url=https://web.archive.org/web/20170123203428/http://www.nfl.com/rulebook/backwardpass |archive-date=January 23, 2017}}</ref> In the NFL, a down also ends immediately if the runner's helmet comes off.<ref name="When a runner's helmet comes off, he's down">{{cite web|last1=Smith|first1=Michael David|title=When a runner's helmet comes off, he's down|url=http://profootballtalk.nbcsports.com/2013/11/16/when-a-runners-helmet-comes-off-hes-down/|publisher=[[Profootballtalk.com]]|access-date=October 19, 2014|date=November 16, 2013|archive-url=https://web.archive.org/web/20141019035720/http://profootballtalk.nbcsports.com/2013/11/16/when-a-runners-helmet-comes-off-hes-down/|archive-date=October 19, 2014|url-status=live}}</ref>

The offense is given a series of four plays, known as [[Down (gridiron football)|downs]]. If the offense advances ten or more yards in the four downs, they are awarded a new set of four downs. If they fail to advance ten yards, possession of the football is turned over to the defense. In most situations, if the offense reaches their fourth down they will [[Punt (American football)|punt]] the ball to the other team, which forces them to begin their drive from farther down the field; if they are in [[field goal range]], they might attempt to score a field goal instead.<ref name="Beginner's Guide to Football" /> A group of officials, the chain crew, keeps track of both the downs and the distance measurements.<ref name="The Orchestration of the Chain Gang">{{cite news|url=https://www.nytimes.com/2009/01/01/sports/football/01chainside.html|title=The Orchestration of the Chain Gang|last=Branch|first=John|date=December 31, 2008|work=[[The New York Times]]|access-date=December 19, 2012|archive-url=https://web.archive.org/web/20121229055115/http://www.nytimes.com/2009/01/01/sports/football/01chainside.html|archive-date=December 29, 2012|url-status=live}}</ref> On television, a yellow line is electronically superimposed on the field to show the first down line to the viewing audience.<ref name="Yellow line">{{cite magazine|url=http://www.popularmechanics.com/outdoors/sports/4301993|title=The Tech Behind the Football's Broadcast-Only First Down Line|last=St. John|first=Allan|date=December 18, 2009|magazine=[[Popular Mechanics]]|access-date=November 2, 2012|archive-url=https://web.archive.org/web/20121213000449/http://www.popularmechanics.com/outdoors/sports/4301993|archive-date=December 13, 2012|url-status=live}}</ref>

===Kicking===
[[File:Connor Barth attempts field goal 8 November 2015 151108-F-ID984-017.jpg|thumb|upright=1|alt=A placekicker attempts a field goal by kicking the ball from the hands of a holder.|[[Tampa Bay Buccaneers]] placekicker [[Connor Barth]] attempts a field goal by kicking the ball from the hands of a holder. This is the standard method to score field goals or extra points.<ref name="PFRA" /><ref name="dropkick_diagram" />]]
There are two categories of kicks in football: scrimmage kicks, which can be executed by the offensive team on any down from behind or on the line of scrimmage,<ref name="NFL Rules 2012, p. 50">NFL Rules 2012, p.&nbsp;50.</ref><ref name="NCAA Rules 2011–2012, p. 34">NCAA Rules 2011–2012, p.&nbsp;34.</ref><ref name="NFHS Rules 2012, p. 32">NFHS Rules 2012, p.&nbsp;32.</ref> and free kicks.<ref name="NFL Rules 2012, p. 6">NFL Rules 2012, p.&nbsp;6.</ref><ref name="NCAA Rules 2011–2012, p. 30">NCAA Rules 2011–2012, p.&nbsp;30.</ref><ref name="NFHS Rules 2012, p. 27">NFHS Rules 2012, p.&nbsp;27.</ref> The free kicks are the [[Kickoff (American football)|kickoff]], which starts the first and third quarters and overtime and follows a try attempt or a successful field goal; the safety kick follows a safety.<ref name="NCAA Rules 2011–2012, p. 34"/><ref name="NFL Rules 2012, pp. 8-9">NFL Rules 2012, pp.&nbsp;8–9.</ref><ref name="NFHS Rules 2012, pp. 31-32">NFHS Rules 2012, pp.&nbsp;31–32.</ref>

On a kickoff, the ball is placed at the 35-yard line of the kicking team in professional and college play and at the 40-yard line in high school play. The ball may be drop kicked or place kicked. If a place kick is chosen, the ball can be placed on the ground or a tee; a holder may be used in either case. On a safety kick, the kicking team kicks the ball from their own 20-yard line. They can punt, drop kick or place kick the ball, but a tee may not be used in professional play. Any member of the receiving team may catch or advance the ball. The ball may be recovered by the kicking team once it has gone at least ten yards and has touched the ground or has been touched by any member of the receiving team.<ref name="NFL Rules 2012, pp. 29-30">NFL Rules 2012, pp.&nbsp;29–30.</ref><ref name="NCAA Rules 2011–2012, pp. 61-64">NCAA Rules 2011–2012, pp.&nbsp;61–64.</ref><ref name="NFHS Rules 2012, pp. 15, 46, 52–53">NFHS Rules 2012, pp.&nbsp;15,&nbsp;46,&nbsp;52–53.</ref>

The three types of scrimmage kicks are place kicks, drop kicks, and punts. Only place kicks and drop kicks can score points.<ref name="NFL Rules 2012, p. 57-59" /><ref name="NCAA Rules 2011–2012, p. 79-80" /><ref name="NFHS Rules 2012, p. 66" /> The place kick is the standard method used to score points,<ref name="PFRA">{{cite journal|last=Hogrogian|first=John|year=1999|title=The Last Drop Kick?|journal=[[The Coffin Corner]]|volume=21|issue=6|url=http://profootballresearchers.com/archives/Website_Files/Coffin_Corner/21-06-832.pdf|access-date=October 22, 2012|archive-url=https://web.archive.org/web/20150618235835/http://profootballresearchers.com/archives/Website_Files/Coffin_Corner/21-06-832.pdf|archive-date=June 18, 2015|url-status=live}}</ref> because the pointy shape of the football makes it difficult to reliably drop kick.<ref name="PFRA" /><ref name="dropkick_diagram">{{cite web|url=http://www.profootballhof.com/hof/release.aspx?release_id=1481|title=Dropkick_diagram|publisher=[[Pro Football Hall of Fame]]|access-date=October 8, 2012|archive-url=https://web.archive.org/web/20121021234605/http://www.profootballhof.com/hof/release.aspx?release_id=1481|archive-date=October 21, 2012|url-status=dead}}</ref> Once the ball has been kicked from a scrimmage kick, it can be advanced by the kicking team only if it is caught or recovered behind the line of scrimmage. If it is touched or recovered by the kicking team beyond this line, it becomes dead at the spot where it was touched.<ref name="NFL Rules 2012, pp. 33-34, 50–53">NFL Rules 2012, pp.&nbsp;33–34,&nbsp;50–53.</ref><ref name="NCAA Rules 2011–2012, pp. 55-56, 63–64">NCAA Rules 2011–2012, pp.&nbsp;55–56,&nbsp;63–64.</ref><ref name="NFHS Rules 2012, pp. 49, 53–54">NFHS Rules 2012, pp.&nbsp;49,&nbsp; 53–54.</ref> The kicking team is prohibited from interfering with the receiver's opportunity to catch the ball. The receiving team has the option of signaling for a [[fair catch]], which prohibits the defense from blocking into or tackling the receiver. The play ends as soon as the ball is caught, and the ball may not be advanced.<ref name="NFL Rules 2012, p. 7">NFL Rules 2012, pp.&nbsp;7,&nbsp;54–55.</ref><ref name="NCAA Rules 2011–2012, pp. 30, 66–67">NCAA Rules 2011–2012, pp.&nbsp;30,&nbsp;66–67.</ref><ref name="NFHS Rules 2012, p. 2756,">NFHS Rules 2012, pp.&nbsp;27,&nbsp;56.</ref>

===Officials and fouls===
{{See also|Official (American football)|Chain crew|Penalty (gridiron football)}}
[[File:American football referees.jpg|thumb|upright=1|alt=Seven officials are pictured meeting at the infield. Officials meeting at midfield |Officials meeting at midfield]]
[[File:First down measurement at EWU at Cal 2009-09-12.JPG|thumb|upright=1|alt=Officials are using a chain to measure for a first down. | Officials use the chains to measure for a first down. Here, the ball is just short of the pole and therefore short of a first down.]]
[[File:First down marker.png|thumb|upright=1|alt=Photograph of a down indicator box on a pole | A modern down indicator box is mounted on a pole and is used to mark the current line of scrimmage. The number on the marker is changed using a dial.]]
Officials are responsible for enforcing game rules and monitoring the clock. All officials carry a [[whistle]] and wear black-and-white striped shirts and black hats except for the referee, whose hat is white. Each carries a [[Penalty flag|weighted yellow flag]] that is thrown to the ground to signal that a [[Penalty (gridiron football)|foul]] has been called. An official who spots multiple fouls will throw their hat as a secondary signal.<ref name="American Football Officials">{{cite web|url=http://www.dummies.com/how-to/content/american-football-officials.html|title=American Football Officials|last1=Long|first1=Howie|last2=Czarnecki|first2=John|author-link1=Howie Long|publisher=[[For Dummies|Dummies.com]]|access-date=November 22, 2012|archive-url=https://web.archive.org/web/20121127034309/http://www.dummies.com/how-to/content/american-football-officials.html|archive-date=November 27, 2012|url-status=live}}</ref> Women can serve as officials; [[Sarah Thomas (American football official)|Sarah Thomas]] became the NFL's first female official in 2015.<ref>{{cite web |last1=Fox |first1=Ashley |title=Meet Sarah Thomas, NFL's first female official |url=https://www.espn.com/nfl/story/_/id/12669370/meet-sarah-thomas-first-female-nfl-official-referee |work=[[ESPN.com]] |language=en |date=April 17, 2015 |access-date=August 10, 2019 |archive-date=August 10, 2019 |archive-url=https://web.archive.org/web/20190810190056/https://www.espn.com/nfl/story/_/id/12669370/meet-sarah-thomas-first-female-nfl-official-referee |url-status=live }}</ref> The seven officials (of a standard seven-man crew; lower levels of play up to the college level use fewer officials) on the field are each tasked with a different set of responsibilities:<ref name="American Football Officials" />
* The '''referee''' is positioned behind and to the side of the offensive backs. The referee is charged with oversight and control of the game and is the authority on the score, the down number, and any rule interpretations in discussions among the other officials. The referee announces all penalties and discusses the infraction with the offending team's captain, monitors for illegal hits against the quarterback, makes requests for first-down measurements, and notifies the head coach whenever a player is ejected. The referee positions themselves to the passing arm side of the quarterback. In most games, the referee is responsible for spotting the football prior to a play from scrimmage.
* The '''umpire''' is positioned in the defensive backfield, except in the NFL, where the umpire is positioned lateral to the referee on the opposite side of the formation. The umpire watches play along the line of scrimmage to make sure that no more than 11 offensive players are on the field before the snap, and that no offensive linemen are [[Ineligible receiver downfield|illegally downfield]] on pass plays. The umpire monitors contact between offensive and defensive linemen and calls most of the [[Holding (American football)|holding]] penalties. The umpire records the number of timeouts taken and the winner of the coin toss and game score. They also assist the referee in situations involving possession of the ball close to the line of scrimmage, determines whether player equipment is legal, and dries wet balls prior to the snap if a game is played in rain.
* The '''back judge''' is positioned deep in the defensive backfield, behind the umpire. The back judge ensures that the defensive team has no more than 11 players on the field and determines whether catches are legal, whether field goal or extra point attempts are good, and whether a [[pass interference]] violation occurred. The back judge is also responsible for the play clock, the time between each play, when a visible play clock is not used.
* The '''head linesman'''/'''down judge''' is positioned on one end of the line of scrimmage. The head linesman/down judge watches for any line-of-scrimmage and illegal use-of-hands violations and assists the line judge with illegal shift or illegal motion calls. The head linesman/down judge also rules on out-of-bounds calls that happen on their side of the field, oversees the chain crew, and marks the forward progress of a runner when a play has been whistled dead.
* The '''side judge''' is positioned twenty yards downfield of the head linesman. The side judge mainly duplicates the functions of the field judge. On field goal and extra point attempts, the side judge is positioned lateral to the umpire.
* The '''line judge''' is positioned on the end of the line of scrimmage, opposite the head linesman. They supervise player substitutions, the line of scrimmage during punts, and game timing. The line judge notifies the referee when time has expired at the end of a quarter and notifies the head coach of the home team when five minutes remain for halftime. In the NFL, the line judge also alerts the referee when [[Two-minute warning|two minutes remain in the half]]. If the clock malfunctions or becomes inoperable, the line judge becomes the official timekeeper.
* The '''field judge''' is positioned twenty yards downfield from the line judge. The field judge monitors and controls the [[play clock]], counts the number of defensive players on the field, and watches for offensive pass interference and illegal use-of-hands violations by offensive players. The field judge also makes decisions regarding catches, recoveries, the ball spot when a player goes out of bounds, and illegal touching of fumbled balls that have crossed the line of scrimmage. On field goal and extra point attempts, the field judge is stationed under the upright opposite the back judge.
* The '''center judge''' is an eighth official used only in the top level of college football. The center judge stands lateral to the referee, the same way the umpire does in the NFL. The center judge is responsible for spotting the football after each play and has many of the same responsibilities as the referee, except announcing penalties.
Another set of officials, the [[chain crew]], are responsible for moving the chains. The chains, consisting of two large sticks with a 10-yard-long chain between them, are used to measure for a first down. The chain crew stays on the sidelines during the game, but if requested by the officials they will briefly bring the chains on to the field to measure. A typical chain crew will have at least three people—two members of the chain crew will hold either of the two sticks, while a third will hold the down marker. The down marker, a large stick with a dial on it, is flipped after each play to indicate the current down and is typically moved to the approximate spot of the ball. The chain crew system has been used for over 100 years and is considered an accurate measure of distance, rarely subject to criticism from either side.<ref name="The Orchestration of the Chain Gang"/>

==Safety and brain health==
{{See also|Protective equipment in gridiron football|Health issues in American football}}
[[File:Vince Agnew.jpg|thumb|upright=1|alt=Photograph of a player wearing a helmet, with shoulder pads and thigh pads visible under their uniform|[[Vince Agnew]] wearing a helmet with his shoulder pads and thigh pads visible under his uniform]]
Football is a full-contact sport, and injuries are relatively common. Most injuries occur during training sessions, particularly ones that involve contact between players.<ref name="Sports Medicine" /> To try to prevent injuries, players are required to wear a set of equipment. At a minimum players must wear a [[football helmet]] and a set of [[Shoulder pads (sport)|shoulder pads]], but individual leagues may require additional padding such as thigh pads and guards, knee pads, chest protectors, and [[mouthguard]]s.<ref name="NFL Rules 2012, pp. 24-27">NFL Rules 2012, pp.&nbsp;24–27.</ref><ref name="NCAA Rules 2011-2012, p. 22">NCAA Rules 2011–2012, p.&nbsp; 22.</ref><ref name="NFHS Rules 2012, pp. 17-19">NFHS Rules 2012, pp.&nbsp;17–19.</ref> Most injuries occur in the lower extremities, particularly in the knee, but a significant number also affect the upper extremities. The most common types of injuries are [[strain (injury)|strains]], [[sprain]]s, [[bruise]]s, fractures, [[Joint dislocation|dislocations]], and [[concussion]]s.<ref name="Sports Medicine">{{cite journal |author=Saal JA |title=Common American football injuries |journal=Sports Medicine |volume=12 |issue=2 |pages=132–47 | date=August 1991 |pmid=1947533 |doi=10.2165/00007256-199112020-00005|s2cid=45077919 }}</ref>

Repeated [[Concussions in American football|concussions]] (and possibly sub-concussive head impacts<ref>{{Cite news |url=https://www.npr.org/sections/health-shots/2018/01/18/578355877/repeated-head-hits-not-concussions-may-be-behind-a-type-of-chronic-brain-damage |title=Repeated Head Hits, Not Just Concussions, May Lead To A Type Of Chronic Brain Damage |website=[[NPR.org]]|access-date=January 20, 2018 |archive-url=https://web.archive.org/web/20180120000839/https://www.npr.org/sections/health-shots/2018/01/18/578355877/repeated-head-hits-not-concussions-may-be-behind-a-type-of-chronic-brain-damage |archive-date=January 20, 2018 |url-status=live  }}</ref>) can increase a person's risk in later life for CTE ([[chronic traumatic encephalopathy]]) and mental health issues such as [[dementia]], [[Parkinson's disease]], and [[Mood disorder|depression]].<ref>{{cite web|last=Maiese|first=Kenneth|work=[[The Merck Manual of Diagnosis and Therapy#The Merck Manual of Medical Information – Home Edition|The Merck Manual Home – Health Handbook]]|url=http://www.merckmanuals.com/home/injuries_and_poisoning/head_injuries/concussion.html?qt=&sc=&alt=|title=Concussion|date=January 2008|access-date=September 2, 2013|archive-url=https://web.archive.org/web/20120915015630/http://www.merckmanuals.com/home/injuries_and_poisoning/head_injuries/concussion.html?qt=&sc=&alt=|archive-date=September 15, 2012|url-status=live}}</ref> Concussions are often caused by helmet-to-helmet or upper-body contact between opposing players, although helmets have prevented more serious injuries such as [[skull fracture]]s.<ref name="Can Football Finally Tackle Its Injury Problem?">{{cite news|url=http://www.time.com/time/nation/article/0,8599,2027053,00.html|title=Can Football Finally Tackle Its Injury Problem?|last=Gregory|first=Sean|date=October 22, 2010|magazine=[[Time (magazine)|Time]]|access-date=January 16, 2013|archive-url=https://web.archive.org/web/20130113062055/http://www.time.com/time/nation/article/0,8599,2027053,00.html|archive-date=January 13, 2013|url-status=dead}}</ref> Various programs are aiming to reduce concussions by reducing the frequency of helmet-to-helmet hits; [[USA Football]]'s "Heads Up Football" program aims to reduce concussions in youth football by teaching coaches and players about the signs of a concussion, the proper way to wear football equipment and ensure it fits, and proper tackling methods that avoid helmet-to-helmet contact.<ref name="Heads Up Football">{{cite web|title=Heads Up Football|url=http://usafootball.com/headsup|publisher=[[USA Football]]|access-date=September 20, 2013|archive-url=https://web.archive.org/web/20130925122045/http://usafootball.com/headsup|archive-date=September 25, 2013|url-status=live}}</ref> However, a study in the ''Orthopaedic Journal of Sports Medicine'' found that Heads Up Football was ineffective; the same study noted that more extensive reforms implemented by [[Pop Warner Little Scholars]] and its member teams were effective in significantly reducing concussion rates.<ref>{{Cite web |url=https://www.nytimes.com/2016/07/28/sports/football/nfl-concussions-youth-program-heads-up-football.html |title=N.F.L.-Backed Youth Program Says It Reduced Concussions. The Data Disagrees. |last=Schwarz |first=Alan |date=July 27, 2016 |website=[[The New York Times]] |url-status=live |archive-url=https://web.archive.org/web/20170208031203/https://www.nytimes.com/2016/07/28/sports/football/nfl-concussions-youth-program-heads-up-football.html |archive-date=February 8, 2017}}</ref>

A 2018 study performed by the VA Boston Healthcare System and the [[Boston University School of Medicine]] found that tackle football before age 12 was correlated with earlier onset of symptoms of CTE, but not with symptom severity. More specifically, each year a player played tackle football under age 12 predicted earlier onset of cognitive, behavioral, and mood problems by an average of two and a half years.<ref name="Study finds youth football tied to earlier symptoms of CTE, ESPN, April 30, 2018">{{Cite web |url=https://www.espn.com/moresports/story/_/id/23367461/study-finds-youth-football-tied-earlier-cte |title=Study finds youth football tied to earlier symptoms of CTE |date=April 30, 2018 |website=[[ESPN]] |url-status=live |archive-url=https://web.archive.org/web/20180623193913/http://www.espn.com/moresports/story/_/id/23367461/study-finds-youth-football-tied-earlier-cte |archive-date=June 23, 2018 |access-date=September 24, 2019}}</ref><ref name="Austin American-Statesman, May 25, 2018">{{Cite web | url=https://www.mystatesman.com/lifestyles/parenting/parents-put-off-tackle-football-long-possible-study-suggests/N0awHDRHeGvbVGaZArxRBM/ |title= Parents, put off tackle football as long as possible, study suggests |last=Villalpando | first=Nicole|website=[[Austin American-Statesman]]|date=May 25, 2018|archive-url=https://web.archive.org/web/20180623193922/https://www.mystatesman.com/lifestyles/parenting/parents-put-off-tackle-football-long-possible-study-suggests/N0awHDRHeGvbVGaZArxRBM/ |archive-date=June 23, 2018}}</ref><ref name="Annals of Neurology, 30 April 2018">[https://onlinelibrary.wiley.com/doi/abs/10.1002/ana.25245 Age of First Exposure to Tackle Football and Chronic Traumatic Encephalopathy] {{Webarchive|url=https://web.archive.org/web/20181215044512/https://onlinelibrary.wiley.com/doi/abs/10.1002/ana.25245 |date=December 15, 2018 }}, ''Annals of Neurology'', Michael L. Alosco PhD, Jesse Mez MD, MS, Yorghos Tripodis PhD, Patrick T. Kiernan BA, Bobak Abdolmohammadi BA, Lauren Murphy BA, Neil W. Kowall MD, Thor D. Stein MD, PhD, Bertrand Russell Huber MD, PhD, Lee E. Goldstein MD, PhD, Robert C. Cantu MD, Douglas I. Katz MD, Christine E. Chaisson MPH, Brett Martin MS, Todd M. Solomon PhD, Michael D. McClean ScD, Daniel H. Daneshvar MD, PhD, Christopher J. Nowinski PhD, Robert A. Stern PhD, Ann C. McKee MD, April 30, 2018.</ref>

==Leagues and tournaments==
[[File:High School Football Game.jpg|thumb|upright=1|A [[high school football]] game]]
The [[National Football League]] (NFL) and the [[National Collegiate Athletic Association]] (NCAA) are the most popular football leagues in the United States.<ref name="Oregon Live">{{cite web|url=http://www.oregonlive.com/ducks/index.ssf/2012/05/head_of_new_usfl_believes_it_c.html|title=New version of United States Football League aims to succeed where others have failed|last=Fentress|first=Andrew|date=May 18, 2012|work=[[OregonLive.com|Oregon Live]]|publisher=[[Advance Internet]]|access-date=January 9, 2013|archive-url=https://web.archive.org/web/20130709033107/http://www.oregonlive.com/ducks/index.ssf/2012/05/head_of_new_usfl_believes_it_c.html|archive-date=July 9, 2013|url-status=live}}</ref> The National Football League was founded in 1920<ref name="NFL founded in Canton">{{cite web|url=http://www.profootballhof.com/history/2005/1/1/nfl-founded-in-canton/|title=NFL founded in Canton|publisher=[[Pro Football Hall of Fame]]|access-date=November 26, 2012|archive-url=https://web.archive.org/web/20130515143229/http://www.profootballhof.com/history/2005/1/1/nfl-founded-in-canton/|archive-date=May 15, 2013|url-status=live}}</ref> and has since become the largest and most popular sport in the United States.<ref name="China fast catching American football fever">{{cite news|url=http://www.scmp.com/sport/china/article/1090060/china-fast-catching-american-football-fever-10-teams-formed|title=China fast catching American football fever with 10 teams formed|last=Chin|first=Andrew|date=November 25, 2012|work=[[South China Morning Post]]|access-date=November 26, 2012|archive-url=https://web.archive.org/web/20170929203100/http://www.scmp.com/sport/china/article/1090060/china-fast-catching-american-football-fever-10-teams-formed|archive-date=September 29, 2017|url-status=live}}</ref> The NFL has the highest average attendance of any sporting league in the world, with an average attendance of 66,960 during the [[2011 NFL season]].<ref name="And the silver goes to...">{{cite news|url=https://www.economist.com/blogs/gametheory/2011/09/ranking-sports%E2%80%99-popularity|title=And the silver goes to&nbsp;...|date=September 27, 2011|newspaper=[[The Economist]]|access-date=December 6, 2012|archive-url=https://web.archive.org/web/20130120230854/http://www.economist.com/blogs/gametheory/2011/09/ranking-sports%E2%80%99-popularity|archive-date=January 20, 2013|url-status=live}}</ref> The NFL championship game is called the Super Bowl, and is among the biggest events in club sports worldwide.<ref name="Elite clubs on Uefa gravy train as Super Bowl knocked off perch">{{cite news|title=Elite clubs on Uefa gravy train as Super Bowl knocked off perch|last=Harris|first=Nick|date=January 31, 2010|work=[[The Independent]]|url=https://www.independent.co.uk/sport/football/european/elite-clubs-on-uefa-gravy-train-as-super-bowl-knocked-off-perch-1884429.html|access-date=November 28, 2012|archive-url=https://web.archive.org/web/20121119135550/http://www.independent.co.uk/sport/football/european/elite-clubs-on-uefa-gravy-train-as-super-bowl-knocked-off-perch-1884429.html|archive-date=November 19, 2012|url-status=live}}</ref> It is played between the champions of the [[National Football Conference]] (NFC) and the [[American Football Conference]] (AFC), and its winner is awarded the [[Vince Lombardi Trophy]].<ref name="Let's Learn About: The Vince Lombardi Trophy">{{cite web|url=http://www.post-gazette.com/stories/sectionfront/life/lets-learn-about-the-vince-lombardi-trophy-356977/|title=Let's Learn About: The Vince Lombardi Trophy|last=George|first=Shannon|date=September 10, 2009|work=[[Pittsburgh Post-Gazette]]|access-date=January 9, 2013|archive-url=https://web.archive.org/web/20121022061816/http://www.post-gazette.com/stories/sectionfront/life/lets-learn-about-the-vince-lombardi-trophy-356977/|archive-date=October 22, 2012|url-status=live}}</ref>

[[College football]] is the third-most popular sport in the United States, behind professional baseball and professional football.<ref name="Harris Poll 2012">{{cite web|url=http://www.harrisinteractive.com/NewsRoom/HarrisPolls/tabid/447/mid/1508/articleId/950/ctl/ReadCustom%20Default/Default.aspx|title=Football is America's Favorite Sport as Lead Over Baseball Continues to Grow|date=January 25, 2005|publisher=[[Harris Insights & Analytics|Harris Interactive]]|access-date=November 26, 2012|archive-url=https://web.archive.org/web/20130127211007/http://www.harrisinteractive.com/NewsRoom/HarrisPolls/tabid/447/mid/1508/articleId/950/ctl/ReadCustom%20Default/Default.aspx|archive-date=January 27, 2013|url-status=dead}}</ref> The NCAA, the largest collegiate organization, is divided into three Divisions: [[NCAA Division I|Division I]], [[NCAA Division II|Division II]] and [[NCAA Division III|Division III]].<ref name="About the NCAA">{{cite web|url=https://www.ncaa.org/wps/wcm/connect/public/NCAA/About+the+NCAA/index.html |title=About the NCAA |publisher=[[National Collegiate Athletic Association|NCAA.org]] |access-date=January 9, 2013 |archive-url=https://web.archive.org/web/20130118120358/http://www.ncaa.org/wps/wcm/connect/public/NCAA/About%2Bthe%2BNCAA/index.html |archive-date=January 18, 2013 |url-status=dead }}</ref> Division I football is further divided into two subdivisions: the [[Football Bowl Subdivision]] (FBS) and the [[Football Championship Subdivision]] (FCS).<ref name="Differences Among the Three Divisions: Division I">{{cite web|url=https://www.ncaa.org/wps/wcm/connect/public/ncaa/about+the+ncaa+old/who+we+are/differences+among+the+divisions/division+i/about+division+i |title=Differences Among the Three Divisions: Division I |publisher=[[National Collegiate Athletic Association|NCAA.org]] |access-date=January 9, 2013 |archive-url=https://web.archive.org/web/20131104204838/http://www.ncaa.org/wps/wcm/connect/public/ncaa/about%2Bthe%2Bncaa%2Bold/who%2Bwe%2Bare/differences%2Bamong%2Bthe%2Bdivisions/division%2Bi/about%2Bdivision%2Bi |archive-date=November 4, 2013 |url-status=dead }}</ref> The champions of each level of play are determined through NCAA-sanctioned playoff systems; while the champion of Division I-FBS was historically determined by various polls and ranking systems, the subdivision adopted a four-team playoff system in 2014.<ref name="Postseason Football">{{cite web|url=https://www.ncaa.org/wps/wcm/connect/public/NCAA/Championships/Postseason+Football/Overview |archive-url=https://web.archive.org/web/20120522204127/http://www.ncaa.org/wps/wcm/connect/public/ncaa/championships/postseason%2Bfootball/overview |url-status=dead |archive-date=May 22, 2012 |title=Postseason Football |publisher=[[National Collegiate Athletic Association|NCAA.org]] |access-date=January 9, 2013 }}</ref>

[[High school football]] is the most popular sport in the United States played by boys; over 1.1&nbsp;million boys participated in the sport from 2007 to 2008 according to a survey by the [[National Federation of State High School Associations]] (NFHS). There is a stark contrast in youth football participation between boys and girls. Only one youth football league exists in the United States for girls, the [[Utah Girls Football League|GFL]]. The NFHS is the largest organization for high school football, with member associations in all [[List of states and territories of the United States|50 states]] as well as the [[Washington, D.C.|District of Columbia]]. USA Football is the governing body for youth and amateur football,<ref name="NFHS and USA Football Create Football Coaching Course">{{cite web|last=Alic|first=Steve|title=NFHS and USA Football Create Football Coaching Course|url=http://usafootball.com/news/press-box/nfhs-and-usa-football-create-football-coaching-course|publisher=[[USA Football]]|access-date=October 5, 2013|date=April 4, 2009|archive-url=https://web.archive.org/web/20131012064911/http://usafootball.com/news/press-box/nfhs-and-usa-football-create-football-coaching-course|archive-date=October 12, 2013|url-status=live}}</ref> and Pop Warner Little Scholars is the largest organization for youth football.<ref name="Trying to Reduce Head Injuries, Youth Football Limits Practices">{{cite news|last=O'Connor|first=Anahad|title=Trying to Reduce Head Injuries, Youth Football Limits Practices|url=https://www.nytimes.com/2012/06/14/sports/pop-warner-football-limits-contact-in-practices.html|newspaper=The New York Times|access-date=October 5, 2013|date=June 12, 2012|archive-url=https://web.archive.org/web/20131012030435/http://www.nytimes.com/2012/06/14/sports/pop-warner-football-limits-contact-in-practices.html|archive-date=October 12, 2013|url-status=live}}</ref>

===Other professional leagues===
====Rival leagues====
The most successful league to directly compete with the NFL was the American Football League (AFL), which existed from 1960 to 1969. The AFL became a significant rival in [[1964 American Football League season|1964]] before signing a five-year, US$36&nbsp;million television deal with NBC. AFL teams began signing NFL players to contracts, and the league's popularity grew to challenge that of the NFL. The two leagues merged in the [[1970 NFL season|1970 season]], and all the AFL teams joined the NFL. An earlier league, the [[All-America Football Conference]] (AAFC), was in play from 1946 to 1949. After it had dissolved, two AAFC teams, the [[Cleveland Browns]] and the [[San Francisco 49ers]], became members of the NFL; another member, the [[Baltimore Colts (1947–50)|Baltimore Colts]] joined the league, but folded after just a year in the NFL.<ref name="Off-the-field competition yields game-changing merger">{{cite web|url=http://sportsillustrated.cnn.com/football/news/2001/01/22/afl_history_2/|title=Off-the-field competition yields game-changing merger|last=Cross|first=B. Duane|date=January 22, 2001|publisher=[[CNN Sports Illustrated|CNNSI]]|access-date=February 15, 2013|archive-url=https://web.archive.org/web/20131019095747/http://sportsillustrated.cnn.com/football/news/2001/01/22/afl_history_2/|archive-date=October 19, 2013}}</ref>

Other attempts to start rival leagues since the AFL merged with the NFL in 1970 have been far less successful, as professional football salaries and the [[NFL on television|NFL's television contracts]] began to escalate out of the reach of competitors and the NFL covered more of the larger cities. The [[World Football League]] (WFL) played for two seasons, in 1974 and 1975, but faced such severe monetary issues it could not pay its players. In its second and final season the WFL attempted to establish a stable credit rating, but the league disbanded before the season could be completed.<ref name="The Day The Money Ran Out">{{cite magazine|url=http://sportsillustrated.cnn.com/vault/article/magazine/MAG1090543/index.htm|title=The Day The Money Ran Out|last=Johnson|first=William Oscar|date=December 1, 1975|magazine=[[Sports Illustrated]]|access-date=March 25, 2013|archive-url=https://web.archive.org/web/20131019095749/http://sportsillustrated.cnn.com/vault/article/magazine/MAG1090543/index.htm|archive-date=October 19, 2013}}</ref> The [[United States Football League]] (USFL) operated for three seasons from 1983 to 1985. Originally not intended as a rival league, the entry of owners who sought marquee talent and to challenge the NFL led to an escalation in salaries and ensuing financial losses. A subsequent US$1.5&nbsp;billion antitrust lawsuit against the NFL was successful in court, but the league was awarded only $1 in damages, which was automatically tripled to $3 under antitrust law.<ref name="Twenty years later, USFL still brings fond memories">{{cite web|url=http://usatoday30.usatoday.com/sports/football/2006-08-07-usfl-retrospective_x.htm|title=Twenty years later, USFL still brings fond memories|last=Somers|first=Kent|date=August 7, 2008|work=[[USA Today]]|access-date=March 25, 2013|archive-url=https://web.archive.org/web/20121023153935/http://usatoday30.usatoday.com/sports/football/2006-08-07-usfl-retrospective_x.htm|archive-date=October 23, 2012|url-status=live}}</ref>

====Complementary national leagues====
The original [[XFL (2001)|XFL]], created in 2001 by [[Vince McMahon]], lasted for only one season. Despite television contracts with NBC and [[UPN]], and high expectations, the XFL suffered from low quality of play and poor reception for its use of [[Attitude Era|tawdry professional wrestling gimmicks]], which caused initially high ratings and attendance to collapse.<ref name="No More Springtimes for the XFL as League Folds">{{cite news|url=https://www.nytimes.com/2001/05/11/sports/pro-football-no-more-springtimes-for-the-xfl-as-league-folds.html|title=No More Springtimes for the XFL as League Folds|last=Sandomir|first=Richard|date=May 11, 2001|newspaper=[[The New York Times]]|access-date=January 20, 2013|archive-url=https://web.archive.org/web/20130515122239/http://www.nytimes.com/2001/05/11/sports/pro-football-no-more-springtimes-for-the-xfl-as-league-folds.html|archive-date=May 15, 2013|url-status=live}}</ref> The XFL was rebooted in [[XFL (2020)|2020]].<ref>{{Cite news|title=The XFL Aims To Capitalize On Spring Football With 9-Point Touchdowns, Other Oddities|url=https://www.npr.org/2020/02/07/802317324/the-xfl-aims-to-capitalize-on-spring-football-with-9-point-touchdowns-other-oddi|access-date=July 15, 2021|website=NPR.org|date=February 7, 2020|language=en|last1=Pascale|first1=Jordan|archive-date=July 15, 2021|archive-url=https://web.archive.org/web/20210715174119/https://www.npr.org/2020/02/07/802317324/the-xfl-aims-to-capitalize-on-spring-football-with-9-point-touchdowns-other-oddi|url-status=live}}</ref> However, after only five weeks of play, the league's operations slowly came to a close due to the ongoing [[COVID-19 pandemic in the United States|COVID-19 pandemic]],<ref name="suspendsoperations">{{cite news|date=April 10, 2020|title=XFL suspends operations, lays off employees and has no plans for 2021 season|website=ESPN.com|url=https://www.espn.com/xfl/story/_/id/29021347/xfl-suspends-all-operations-lays-employees-amid-coronavirus-pandemic|access-date=April 10, 2020|archive-date=May 24, 2021|archive-url=https://web.archive.org/web/20210524185119/https://www.espn.com/xfl/story/_/id/29021347/xfl-suspends-all-operations-lays-employees-amid-coronavirus-pandemic|url-status=live}}</ref> and filed for bankruptcy on April 13.<ref name="seekingbuyer">{{cite news|date=April 13, 2020|title=XFL Files for Bankruptcy, Up for Sale|website=The Hollywood Reporter|url=https://www.hollywoodreporter.com/live-feed/vince-mcmahons-xfl-files-bankruptcy-up-sale-1290073|access-date=April 13, 2020|archive-date=February 15, 2022|archive-url=https://web.archive.org/web/20220215012453/https://www.hollywoodreporter.com/tv/tv-news/vince-mcmahons-xfl-files-bankruptcy-up-sale-1290073/|url-status=live}}</ref> The [[United Football League (2009–2012)|United Football League]] (UFL) began in [[2009 UFL season|2009]] but folded after suspending its [[2012 UFL season|2012 season]] amid declining interest and lack of major television coverage.<ref name="Just What Is Going on with the UFL?">{{cite web|url=http://www.ibtimes.com/sportsnet/just-what-going-ufl-850157|title=Just What Is Going on with the UFL?|last=Keiser|first=Thomas|date=October 20, 2012|work=[[International Business Times]]|access-date=January 20, 2013|archive-url=https://web.archive.org/web/20121023001718/http://www.ibtimes.com/sportsnet/just-what-going-ufl-850157|archive-date=October 23, 2012|url-status=live}}</ref> The [[Alliance of American Football]] lasted [[2019 AAF season|less than one season]], unable to keep investors.<ref name=disappointed>{{cite news |url=http://www.espn.com/espn/story/_/id/26423928/aaf-suspends-operations-polian-disappointed |title=AAF suspends operations; Polian 'disappointed' |first=Michael |last=Rothstein |website=[[ESPN]] |date=April 3, 2019 |access-date=February 17, 2020 |archive-date=February 16, 2020 |archive-url=https://web.archive.org/web/20200216231033/https://www.espn.com/espn/story/_/id/26423928/aaf-suspends-operations-polian-disappointed |url-status=live }}</ref>

===International play===
[[File:03042012Ccm gamosuma juvenilA366.JPG|thumb|upright=1|alt=Photograph of a Mexican youth division football team|Players with one of the youth divisions of the [[Borregos Salvajes]] football program of the [[Monterrey Institute of Technology and Higher Education, Mexico City]]]]
American football leagues exist throughout the world, but the game has yet to achieve the international success and popularity of [[baseball]] and [[basketball]].<ref>Nelson 1993, p.&nbsp;15.</ref> It is not an [[Olympic sport]], but it was a [[demonstration sport]] at the [[American football at the 1932 Summer Olympics|1932 Summer Olympics]].<ref name="Football remains an Olympic long shot">{{cite web|url=http://profootballtalk.nbcsports.com/2012/07/27/football-remains-an-olympic-longshot/|title=Football remains an Olympic long shot|last=Florio|first=Mike|date=July 27, 2012|work=Pro Football Talk|publisher=[[NBC Sports]]|access-date=January 14, 2013|archive-url=https://web.archive.org/web/20121230101702/http://profootballtalk.nbcsports.com/2012/07/27/football-remains-an-olympic-longshot/|archive-date=December 30, 2012|url-status=live}}</ref> At the international level, Canada, Mexico, and Japan are considered to be second-tier, while Austria, Germany, and France would rank among a third tier. These countries rank far below the United States, which is dominant at the international level.<ref name="Football in Olympics is a dream that could become a reality">{{cite web |last=Breer |first=Albert |date=July 26, 2012 |title=Football in Olympics is a dream that could become a reality |url=http://www.nfl.com/news/story/09000d5d82acf42b/article/football-in-olympics-is-a-dream-that-could-become-a-reality |url-status=live |archive-url=https://web.archive.org/web/20130412185114/http://www.nfl.com/news/story/09000d5d82acf42b/article/football-in-olympics-is-a-dream-that-could-become-a-reality |archive-date=April 12, 2013 |access-date=March 21, 2013 |website=[[National Football League|NFL.com]]}}</ref>

[[NFL Europe|NFL Europa]], the [[minor league|developmental league]] of the NFL, operated from 1991 to 1992 and then from 1995 to 2007. At the time of its closure, NFL Europa had five teams based in Germany and one in the Netherlands.<ref name="NFL Europa to cease operations">{{cite web|title=NFL Europa to cease operations |date=June 29, 2007 |website=[[National Football League|NFL.com]] |archive-url=https://web.archive.org/web/20070703064828/http://www.nfl.com/news/story/10240829 |archive-date=July 3, 2007 |access-date=January 9, 2013 |url=http://www.nfl.com/news/story/10240829 |url-status=dead }}</ref> In Germany, the [[German Football League]] (GFL) has 16 teams and has operated for over 40 seasons, with the league's championship game, the [[German Bowl]], closing out each season. The league operates in a [[promotion and relegation]] structure with [[German Football League 2]] (GFL2), which also has 16 teams.<ref name="Vicksburg" /> The [[BIG6 European Football League]] functions as a continental championship for Europe. The competition is contested between the top six European teams.<ref name="Vicksburg">{{cite web |last1=Bowker |first1=Ernest |title=Ex-VHS football star Johnson carves out career in Germany – The Vicksburg Post |url=https://www.vicksburgpost.com/2018/07/06/ex-vhs-football-star-johnson-carves-out-career-in-germany/ |website=Vicksburg Post |access-date=August 8, 2019 |date=July 6, 2018 |archive-date=August 8, 2019 |archive-url=https://web.archive.org/web/20190808140841/https://www.vicksburgpost.com/2018/07/06/ex-vhs-football-star-johnson-carves-out-career-in-germany/ |url-status=live }}</ref>

The [[United Kingdom]] also operated several teams within NFL Europe during the League's tenure.<ref>{{Cite web|url=https://www.sportingnews.com/us/nfl/news/remembering-the-world-league-of-american-football-nfl-first-big-move-to-europe/k65tsahgc8uf1slkipr8ki55d|title=Remembering the World League of American Football, NFL's first big move to Europe|website=www.sportingnews.com|date=March 23, 2020 |access-date=February 12, 2021|archive-date=November 24, 2021|archive-url=https://web.archive.org/web/20211124111844/https://www.sportingnews.com/us/nfl/news/remembering-the-world-league-of-american-football-nfl-first-big-move-to-europe/k65tsahgc8uf1slkipr8ki55d|url-status=live}}</ref> The resulting rise in popularity of the sport brought the NFL back to the country in 2007 where they now hold the [[NFL International Series]] in [[London]], currently consisting of four regular season games.<ref>{{Cite news|url=http://www.espn.com/nfl/story/_/id/25125916/nfl-play-four-regular-season-games-london-next-year|title=NFL adds fourth game to London slate in 2019|work=ESPN.com|access-date=October 30, 2018|archive-date=October 30, 2018|archive-url=https://web.archive.org/web/20181030185221/http://www.espn.com/nfl/story/_/id/25125916/nfl-play-four-regular-season-games-london-next-year|url-status=live}}</ref><ref>{{cite web|last1=Gordon|first1=Grant|title=NFL announces matchups for international games|url=http://www.nfl.com/news/story/0ap3000001012393/article/nfl-announces-matchups-for-international-games|website=NFL|publisher=NFL Enterprises LLC.|access-date=January 21, 2019|archive-date=January 21, 2019|archive-url=https://web.archive.org/web/20190121232651/http://www.nfl.com/news/story/0ap3000001012393/article/nfl-announces-matchups-for-international-games|url-status=live}}</ref> The continuing interest and growth in both the sport and the series has led to the possible formation of a [[Potential London NFL franchise|potential NFL franchise in London]]<ref>{{Cite magazine|url=https://www.si.com/nfl/2014/10/02/nfl-team-in-london-international-series|title=Why London? And Can It Work?|first=Jenny|last=Vrentas|magazine=Sports Illustrated|access-date=February 12, 2021|archive-date=November 11, 2020|archive-url=https://web.archive.org/web/20201111182115/https://www.si.com/nfl/2014/10/02/nfl-team-in-london-international-series|url-status=live}}</ref><ref>{{Cite web|url=https://www.espn.co.uk/nfl/story/_/id/25124631/how-close-london-getting-nfl-franchise|title=How close is London to getting an NFL franchise?|date=October 30, 2018|website=ESPN.com|access-date=February 12, 2021|archive-date=June 9, 2019|archive-url=https://web.archive.org/web/20190609090636/https://www.espn.co.uk/nfl/story/_/id/25124631/how-close-london-getting-nfl-franchise|url-status=live}}</ref><ref>{{Cite news|url=https://www.bbc.co.uk/sport/american-football/35360989|title=UK-based NFL team 'on track for 2022'|work=BBC Sport |access-date=February 12, 2021|archive-date=December 1, 2020|archive-url=https://web.archive.org/web/20201201134824/https://www.bbc.co.uk/sport/american-football/35360989|url-status=live}}</ref>

An American football league system already exists within the UK, the [[BAFA National Leagues|BAFANL]], which has run under various guises since 1983. It currently has 70 teams operating across the tiers of contact football in which teams aim to earn promotion to the Division above, with the Premier Division teams competing to win the [[Britbowl]], the annual British Football Bowl game that has been played since 1985.<ref>{{Cite web|url=https://www.britishamericanfootball.org/|title=British American Football|access-date=February 11, 2021|archive-date=January 25, 2021|archive-url=https://web.archive.org/web/20210125063038/https://www.britishamericanfootball.org/|url-status=live}}</ref><ref>{{Cite web|url=https://www.footballamerica.co.uk/en/blog/britbowl-33-review|title=Football America UK &#124; Britbowl 33 Review|website=www.footballamerica.co.uk|access-date=February 12, 2021|archive-date=February 15, 2022|archive-url=https://web.archive.org/web/20220215012459/https://www.footballamerica.co.uk/en/blog/britbowl-33-review|url-status=live}}</ref><ref>{{Cite web|url=http://ninetynineyards.com/2019/08/30/britbowl-xxxiii-warriors-v-phoenix/|title=BritBowl XXXIII - Warriors v Phoenix|date=August 30, 2019|website=Ninety-Nine Yards: American Football|access-date=February 12, 2021|archive-date=May 16, 2021|archive-url=https://web.archive.org/web/20210516030710/https://ninetynineyards.com/2019/08/30/britbowl-xxxiii-warriors-v-phoenix/|url-status=live}}</ref> In 2007, the [[British Universities American Football League]] was formed. From 2008, the BUAFL was officially associated with the [[National Football League]] (NFL), through its partner organization NFL UK.<ref>{{cite web|archive-url=https://web.archive.org/web/20110108180209/http://www.nfluk.com/news/NFLBUAFL_121108.html |archive-date=January 8, 2011 |date=November 12, 2008 |url=http://www.nfluk.com/news/NFLBUAFL_121108.html |title=NFL announces partnership with BUAFL |url-status=dead }}</ref> In 2012, BUAFL's league and teams were absorbed into BUCS after American football became an official BUCS sport.<ref>{{Cite web |url=http://www.bucs.org.uk/sport.asp?section=16641tab=1 |title=American Football - British Universities & Colleges Sport |access-date=March 11, 2013 |archive-url=https://web.archive.org/web/20140912144705/http://www.bucs.org.uk/sport.asp?section=16641tab=1 |archive-date=September 12, 2014 |url-status=dead }}</ref> Over the period 2007 to 2014, the BUAFL grew from 42 teams and 2,460 participants to 75 teams and over 4,100 people involved.<ref>{{cite news|url=https://www.independent.co.uk/sport/general/others/super-bowl-2014-move-over-wayne-rooney-gridirons-here-9101644.html|quote=The British Universities American Football League (BUAFL) had 42 teams before the first Wembley game in 2007 and 2,460 participants; now 75 universities are registered, with more than 4,100 players, coaches and officials|title=Super Bowl 2014: Move over, Wayne Rooney – gridiron's here|work=[[The Independent]]|date=February 1, 2014|author=Zander Swinburne|access-date=February 12, 2021|archive-date=April 1, 2019|archive-url=https://web.archive.org/web/20190401193918/https://www.independent.co.uk/sport/general/others/super-bowl-2014-move-over-wayne-rooney-gridirons-here-9101644.html|url-status=live}}</ref>

American football federations are present in [[IFAF Africa|Africa]], [[IFAF Americas|the Americas]], [[IFAF Asia|Asia]], [[IFAF Europe|Europe]], and [[IFAF Oceania|Oceania]]; a total of 75 national football federations exist {{As of|2023|lc=y}}.<ref>{{Cite web |title=Member Federations |url=https://www.americanfootball.sport/member-federations/ |access-date=2024-01-11 |website=International Federation of American Football |language=en-GB}}</ref> The [[International Federation of American Football]] (IFAF), an international governing body composed of continental federations, runs tournaments such as the [[IFAF World Championship]], the [[IFAF Women's World Championship]], the [[IFAF U-19 World Cup|IFAF U-19 World Championship]], and the [[IFAF Flag Football World Championship|Flag Football World Championship]]. The IFAF also organizes the annual International Bowl game.<ref name="Championship Competitions">{{cite web|url=http://www.ifaf.info/pages/competition|title=Championship Competitions|publisher=[[International Federation of American Football]]|access-date=January 9, 2013|archive-url=https://web.archive.org/web/20130625140013/http://www.ifaf.info/pages/competition|archive-date=June 25, 2013|url-status=live}}</ref> The IFAF has received provisional recognition from the [[International Olympic Committee]] (IOC).<ref name="Football takes step toward Olympics, could be medal sport in 2024">{{cite web|url=http://www.foxsports.com/nfl/story/american-football-provisional-recognition-international-olympic-committee-possible-medal-sport-2024-121013|last1=Marvez|first1=Alex|title=Football takes step toward Olympics, could be medal sport in 2024|work=[[Foxsports.com]]|access-date=June 18, 2015|date=June 2, 2014|archive-url=https://web.archive.org/web/20150204060852/http://www.foxsports.com/nfl/story/american-football-provisional-recognition-international-olympic-committee-possible-medal-sport-2024-121013|archive-date=February 4, 2015}}</ref> Several major obstacles hinder the IFAF goal of achieving status as an Olympic sport. These include the predominant participation of men in international play and the short three-week Olympic schedule. Large team sizes are an additional difficulty, due to the Olympics' set limit of 10,500 athletes and coaches. American football also has an issue with a lack of global visibility. [[Nigel Melville]], the CEO of [[USA Rugby]], noted that "American football is recognized globally as a sport, but it's not played globally." To solve these concerns, major effort has been put into promoting [[flag football]], a modified version of American football, at the international level.<ref name="Football in Olympics is a dream that could become a reality" /> Flag football has been shortlisted for appearance at the [[2028 Summer Olympics]], pending final approval by the [[International Olympic Committee]].<ref name="Football (albeit flag) appears finally set for Olympics">{{cite web |last1=Florio |first1=Mike |title=Football (albeit flag) appears finally set for Olympics |url=https://www.nbcsports.com/nfl/profootballtalk/rumor-mill/news/football-albeit-flag-appears-finally-set-for-olympics |website=[[NBC Sports]] |access-date=October 9, 2023 |date=October 9, 2023}}</ref>

==Popularity and cultural influence==
===United States===
{{main|American football in the United States}}
[[File:Alberstson's Stadium Record Attendance for Boise State Football in October 2019.jpg|thumb|upright=1|The [[Boise State Broncos]] are the first football team to design a blue field in 1986.]]
"Baseball is still called the national pastime, but football is by far the more popular sport in American society", according to ESPN.com's Sean McAdam.<ref name="Football leaving baseball in the dust">{{cite web|last=McAdam|first=Sean|title=Football leaving baseball in the dust|url=http://sports.espn.go.com/mlb/columns/story?id=1731732|work=[[ESPN.com]]|access-date=April 17, 2014|date=February 10, 2004|archive-url=https://web.archive.org/web/20140419012854/http://sports.espn.go.com/mlb/columns/story?id=1731732|archive-date=April 19, 2014|url-status=live}}</ref> In a 2014 poll conducted by [[Harris Insights & Analytics|Harris Interactive]], professional football ranked as the most popular sport, and college football ranked third behind only professional football and baseball; 46% of participants ranked some form of the game as their favorite sport. Professional football has ranked as the most popular sport in the poll since 1985, when it surpassed baseball for the first time.<ref name="NFL most popular for 30th year in row">{{cite web|url=http://espn.go.com/nfl/story/_/id/10354114/harris-poll-nfl-most-popular-mlb-2nd|title=NFL most popular for 30th year in row|last=Rovell|first=Darren|date=January 26, 2014|work=[[ESPN.com]]|access-date=March 20, 2013|archive-url=https://web.archive.org/web/20140126180825/http://espn.go.com/nfl/story/_/id/10354114/harris-poll-nfl-most-popular-mlb-2nd|archive-date=January 26, 2014|url-status=live}}</ref> Professional football is most popular among those who live in the eastern United States and rural areas, while college football is most popular in the southern United States and among people with graduate and post-graduate degrees.<ref name="As American as Mom, Apple Pie and Football?">{{cite web|title=As American as Mom, Apple Pie and Football?|url=http://www.harrisinteractive.com/NewsRoom/HarrisPolls/tabid/447/mid/1508/articleId/1365/ctl/ReadCustom%20Default/Default.aspx|publisher=[[Harris Insights & Analytics|Harris Interactive]]|access-date=April 27, 2014|date=January 16, 2014|archive-url=https://web.archive.org/web/20140427115738/http://www.harrisinteractive.com/NewsRoom/HarrisPolls/tabid/447/mid/1508/articleId/1365/ctl/ReadCustom%20Default/Default.aspx|archive-date=April 27, 2014|url-status=dead}}</ref> Football is also the most-played sport by high school and college athletes in the United States. {{as of|2022}}, the [[National Football Foundation]] reports nearly 1.04&nbsp;million high-school athletes play the sport, with another 81,000 college athletes across both the [[National Collegiate Athletic Association|NCAA]] and the [[National Association of Intercollegiate Athletics|NAIA]];<ref name=":0" /> in comparison, the second-most played sport, basketball, had around 920,000 participants in high school and 63,000 in college.<ref>{{Cite web |date=2020-08-31 |title=Basketball Scholarships & Chances of Playing in College {{!}} Scholarship Stats.com |url=https://scholarshipstats.com/basketball |access-date=2024-01-12 |language=en-US}}</ref>

The Super Bowl is the most popular single-day sporting event in the United States,<ref name="The Second 25 Years" /> and is among the biggest club sporting events in the world in terms of TV viewership.<ref name="Elite clubs on Uefa gravy train as Super Bowl knocked off perch" /> The NFL made approximately $12&nbsp;billion in revenue in 2022.<ref>{{Cite web |last=Ozanian |first=Mike |title=NFL National Revenue Was Almost $12 Billion In 2022 |url=https://www.forbes.com/sites/mikeozanian/2023/07/11/nfl-national-revenue-was-almost-12-billion-in-2022/ |access-date=2024-01-12 |website=Forbes |language=en}}</ref> Super Bowl games account for eight of the top ten [[List of most watched television broadcasts in the United States|most-watched broadcasts in American history]]; [[Super Bowl LVII]], played on February 12, 2023, was watched by a record 115.1&nbsp;million Americans,<ref name="Super Bowl XLIX">{{cite web|last1=Peralta|first1=Eyder|title=Super Bowl XLIX Was Most Watched Show in TV History|url=https://www.npr.org/sections/thetwo-way/2015/02/02/383352809/super-bowl-xlix-was-most-watched-show-in-tv-history|publisher=[[NPR]]|access-date=June 18, 2015|date=February 2, 2015|archive-url=https://web.archive.org/web/20150618235512/http://www.npr.org/sections/thetwo-way/2015/02/02/383352809/super-bowl-xlix-was-most-watched-show-in-tv-history|archive-date=June 18, 2015|url-status=live}}</ref> and is second only to the [[Apollo 11]] [[moon landing]] (125&nbsp;million viewers).<ref>{{Cite web |date=2009-08-19 |title=Buzz Aldrin to accept NASA's Emmy award |url=https://www.nbcnews.com/id/wbna32469279 |access-date=2024-01-12 |website=NBC News |language=en}}</ref>

American football also plays a significant role in American culture. The day on which the Super Bowl is held is considered [[Super Bowl Sunday|a ''de facto'' national holiday]],<ref name="NFL has made Super Bowl Sunday into a holiday, is a three-day weekend the next step?">{{cite news|url=https://latimesblogs.latimes.com/entertainmentnewsbuzz/2011/02/nfl-has-made-super-bowl-sunday-into-a-holiday-is-a-three-day-weekend-the-next-step.html|last=Flint|first=Joe|title=NFL has made Super Bowl Sunday into a holiday, is a three-day weekend the next step?|work=[[Los Angeles Times]]|date=February 4, 2011|access-date=September 24, 2019|archive-date=November 16, 2018|archive-url=https://web.archive.org/web/20181116022739/https://latimesblogs.latimes.com/entertainmentnewsbuzz/2011/02/nfl-has-made-super-bowl-sunday-into-a-holiday-is-a-three-day-weekend-the-next-step.html|url-status=live}}</ref> and in parts of the country like [[Texas]], the sport has been compared to a religion.<ref name="In Texas, High School Football Is King">{{cite web|last=Brown|first=Bob|title=In Texas, High School Football Is King|url=https://abcnews.go.com/Primetime/story?id=132425|work=[[ABC News]]|access-date=April 27, 2014|date=January 6, 2006|archive-url=https://web.archive.org/web/20140427141134/https://abcnews.go.com/Primetime/story?id=132425|archive-date=April 27, 2014|url-status=live}}</ref><ref name="A $60 Million Palace for Texas High School Football">{{cite news|last=Bishop|first=Greg|title=A$60 Million Palace for Texas High School Football|url=https://www.nytimes.com/2011/01/30/sports/30allen.html|newspaper=[[The New York Times]]|access-date=April 27, 2014|date=January 29, 2011|archive-url=https://web.archive.org/web/20140514235913/http://www.nytimes.com/2011/01/30/sports/30allen.html|archive-date=May 14, 2014|url-status=live}}</ref> Football is also linked to other holidays; New Year's Day is traditionally the date for several college football bowl games, including the [[Rose Bowl Game|Rose Bowl]]. However, if New Year's Day is on a Sunday, the bowl games are moved to another date so as not to conflict with the typical NFL Sunday schedule.<ref name="No New Year's Day Bowl Games? Bah, Humbug">{{cite web|last=Wischnowsky|first=Dave|title=No New Year's Day Bowl Games? Bah, Humbug|url=http://chicago.cbslocal.com/2011/12/30/wisch-no-new-years-day-bowl-games-bah-humbug/|publisher=[[CBS Chicago]]|access-date=April 28, 2014|date=December 30, 2011|archive-url=https://web.archive.org/web/20140429050123/http://chicago.cbslocal.com/2011/12/30/wisch-no-new-years-day-bowl-games-bah-humbug/|archive-date=April 29, 2014|url-status=live}}</ref> [[Thanksgiving (United States)|Thanksgiving]] [[American football on Thanksgiving|football]] is another American tradition,<ref name="From Macy's to NFL, Thanksgiving traditions explained">{{cite web|last=Lee|first=Jolie|title=From Macy's to NFL, Thanksgiving traditions explained|url=https://www.usatoday.com/story/news/nation-now/2013/11/26/thanksgiving-traditions-history/3709209/|work=[[USA Today]]|access-date=April 28, 2014|date=November 28, 2013|archive-url=https://web.archive.org/web/20131203213114/http://www.usatoday.com/story/news/nation-now/2013/11/26/thanksgiving-traditions-history/3709209/|archive-date=December 3, 2013|url-status=live}}</ref> hosting many high school, college, and professional games.<ref name="Thanksgiving and Football: A Unique American Tradition">{{cite web|last=Bell|first=Danna|title=Thanksgiving and Football: A Unique American Tradition|url=http://blogs.loc.gov/teachers/2012/11/thanksgiving-and-football-a-unique-american-tradition/|publisher=[[Library of Congress]]|access-date=April 28, 2014|date=November 22, 2012|archive-url=https://web.archive.org/web/20140429061739/http://blogs.loc.gov/teachers/2012/11/thanksgiving-and-football-a-unique-american-tradition/|archive-date=April 29, 2014|url-status=live}}</ref> Implicit rules such as playing through pain and sacrificing for the better of the team are promoted in football culture.<ref>Smith (2009), p. 146.</ref>

===Other countries===
{{see also|American football in Japan|American football in the United Kingdom}}
[[File:NFL_International_Series_2010.jpg|thumb|upright=1|alt= Photograph of London's Wembley Stadium during the opening ceremony of the 2010 NFL International series showing the field and the stands filled with fans | Opening ceremony of the 2010 [[NFL International Series]] at London's [[Wembley Stadium]]]]
[[File:Suomi-ruotsi jenkkifutis.jpg|thumb|upright=1|A 2012 football match between national teams of [[Finland]] and [[Sweden]] at [[Sonera Stadium]] (now Bolt Arena) in [[Helsinki]]]]
In [[Canada]], the game has a significant following. According to a 2013 poll, 21% of respondents said they followed the NFL "very closely" or "fairly closely", making it the third-most followed league behind the [[National Hockey League]] (NHL) and [[Canadian Football League]] (CFL).<ref name="Super Bowl 2014: Comparing the NFL's popularity in Canada and the U.S.">{{cite web |last=Spurrier |first=Guy |title=Super Bowl 2014: Comparing the NFL's popularity in Canada and the U.S. |url=http://sports.nationalpost.com/2014/01/30/super-bowl-2014-comparing-the-nfls-popularity-in-canada-and-the-u-s/ |work=[[National Post]] |access-date=April 17, 2014 |date=January 30, 2014 |url-status=dead |archive-url=https://wayback.archive-it.org/all/20170525152429/http://news.nationalpost.com/sports/nfl/super-bowl-2014-comparing-the-nfls-popularity-in-canada-and-the-u-s |archive-date=May 25, 2017 }}</ref> American football also has a long history in Mexico, which was introduced to the sport in 1896. It was the second-most popular sport in Mexico in the 1950s, with the game being particularly popular in colleges.<ref name="Mexico's long love affair with football, American-style">{{cite web|last=Viruega|first=Pablo|title=Mexico's long love affair with football, American-style|url=http://sports.espn.go.com/espn/hispanicheritage2008/news/story?id=3620057|work=[[ESPN.com]]|access-date=April 17, 2014|date=October 1, 2008|archive-url=https://web.archive.org/web/20141005042813/http://sports.espn.go.com/espn/hispanicheritage2008/news/story?id=3620057|archive-date=October 5, 2014|url-status=live}}</ref> The ''[[Los Angeles Times]]'' notes the NFL claims over 16&nbsp;million fans in Mexico, which places the country third behind the U.S. and Canada.<ref name="NFL's popularity in Mexico continues to grow">{{cite news|last=Baxter|first=Kevin|title=NFL's popularity in Mexico continues to grow|url=http://articles.latimes.com/2010/jan/29/sports/la-sp-nfl-mexico29-2010jan29|newspaper=[[Los Angeles Times]]|access-date=April 17, 2014|date=January 29, 2010|archive-url=https://web.archive.org/web/20140418234532/http://articles.latimes.com/2010/jan/29/sports/la-sp-nfl-mexico29-2010jan29|archive-date=April 18, 2014|url-status=live}}</ref> American football is played in Mexico both professionally and as part of the college sports system.<ref name="American football touches down in Germany">{{cite web|title=American football touches down in Germany|url=http://www.thelocal.de/20130127/47579|work=[[The Local]]|access-date=April 17, 2014|date=January 27, 2013|archive-url=https://web.archive.org/web/20140419012014/http://www.thelocal.de/20130127/47579|archive-date=April 19, 2014|url-status=live}}</ref> A professional league, the [[Liga de Fútbol Americano Profesional]] (LFA), was founded in 2016.<ref>{{cite web |last1=Janowitz |first1=Nathaniel |title=Fledgling pro league trying to gain foothold with Mexico's NFL fans |url=https://www.espn.com/nfl/story/_/id/19144594/second-year-professional-football-league-lfa-tries-gain-foothold-mexico-large-nfl-fan-base |publisher=[[ESPN]] |access-date=August 3, 2019 |date=April 14, 2017 |archive-date=August 3, 2019 |archive-url=https://web.archive.org/web/20190803191229/https://www.espn.com/nfl/story/_/id/19144594/second-year-professional-football-league-lfa-tries-gain-foothold-mexico-large-nfl-fan-base |url-status=live }}</ref>

[[Japan]] was introduced to the sport in 1934 by [[Paul Rusch]], a teacher and Christian missionary who helped to establish football teams at three universities in Tokyo.<ref name="Friday night lights: American football in Japan a high school hit">{{cite web|last=Jardine|first=Lisa|title=Friday night lights: American football in Japan a high school hit|url=http://travel.cnn.com/tokyo/play/friday-night-lights-japanese-american-football-player-dream-686573|publisher=[[CNN Travel]]|access-date=April 23, 2014|date=September 28, 2010|archive-url=https://web.archive.org/web/20140417200538/http://travel.cnn.com/tokyo/play/friday-night-lights-japanese-american-football-player-dream-686573|archive-date=April 17, 2014|url-status=live}}</ref> Play was halted during [[World War II]] by order of [[Emperor of Japan|Emperor]] [[Hirohito]], but the sport began growing in popularity again after the war.<ref name="On an Impulse: Josh Cox’s journey to success in Japan’s X-League" /> {{as of|2010}}, there are more than 400 high school football teams in Japan, with over 15,000 participants, and over 100 teams play in the Kantoh Collegiate Football Association (KCFA).<ref name="Friday night lights: American football in Japan a high school hit" /> The [[X-League (Japan)|X-League]] is the largest American football league in Japan, and the largest American football league in the world to use a promotion-relegation system. Some teams in the X-League, like the [[Panasonic Impulse]], are sponsored by corporations, and all Japanese players on these teams are employed by the corporation. The league operates in separate spring and fall seasons, with each team playing five games. The top eight teams make the playoffs, which are played in [[Tokyo Dome]]; the champion is determined by the [[Rice Bowl]].<ref name="On an Impulse: Josh Cox’s journey to success in Japan’s X-League">{{cite web |last1=Jimenez |first1=James H. |title=On an Impulse: Josh Cox's journey to success in Japan's X-League |url=https://www.hustlebelt.com/2023/6/19/23546856/josh-cox-cornerback-panasonic-impulse-japan-x-league-american-football-profile-history |website=Hustle Belt |publisher=[[SB Nation]] |access-date=October 10, 2023 |language=en |date=June 19, 2023}}</ref> 

Europe is a major target for the expansion of the game by football organizers. In the United Kingdom in the 1980s, the sport was popular, with the 1986 Super Bowl being watched by over four million people (about 1 out of every 14 Britons). Its popularity faded during the 1990s, coinciding with the establishment of the [[Premier League]]—top level of the [[English football league system]]. According to [[BBC America]], there is a "social stigma" surrounding American football in the UK, with many Brits feeling the sport has no right to call itself "football" due to the lack of emphasis on kicking.<ref name="Touchdown in the U.K.: Britain's Long-Distance Affair with the NFL">{{cite web|last=Langford|first=John|title=Touchdown in the U.K.: Britain's Long-Distance Affair with the NFL|url=http://www.bbcamerica.com/anglophenia/2014/02/touchdown-u-k-british-nfl-fans-cope-long-distance-love-affair/|publisher=[[BBC America]]. Anglophenia|access-date=April 17, 2014|date=February 17, 2014|archive-url=https://web.archive.org/web/20141110003109/http://www.bbcamerica.com/anglophenia/2014/02/touchdown-u-k-british-nfl-fans-cope-long-distance-love-affair/|archive-date=November 10, 2014|url-status=live}}</ref> Nonetheless, the sport has retained a following in the United Kingdom; the NFL operates a media network in the country, and since 2007 has hosted the [[NFL International Series]] in London. Super Bowl viewership has also rebounded, with over 4.4&nbsp;million Britons watching [[Super Bowl XLVI]].<ref name="Super Bowl caps UK's growing gridiron fever">{{cite web|last1=Morrison|first1=Sarah|last2=Hayman-Brown|first2=Isabel|title=Super Bowl caps UK's growing gridiron fever|url=https://www.independent.co.uk/sport/general/others/super-bowl-caps-uks-growing-gridiron-fever-6423166.html|website=[[The Independent]]|access-date=June 19, 2015|date=February 5, 2012|archive-url=https://web.archive.org/web/20150705211444/http://www.independent.co.uk/sport/general/others/super-bowl-caps-uks-growing-gridiron-fever-6423166.html|archive-date=July 5, 2015|url-status=live}}</ref> The sport is played in European countries like Switzerland, which has American football clubs in every major city,<ref name="The Game Is American, but the View, Alpine">{{cite news|last=Tagliabue|first=John|title=The Game Is American, but the View, Alpine|url=https://www.nytimes.com/2011/04/15/world/europe/15swiss.html|newspaper=[[The New York Times]]|access-date=April 17, 2014|date=April 14, 2011|archive-url=https://web.archive.org/web/20150607082047/http://www.nytimes.com/2011/04/15/world/europe/15swiss.html|archive-date=June 7, 2015|url-status=live}}</ref> and Germany, where the sport has around 45,000 registered amateur players.<ref name="American football touches down in Germany" />

In [[American football in Brazil|Brazil]], football is a growing sport. It was generally unknown there until the 1980s when a small group of players began playing on [[Copacabana Beach]] in [[Rio de Janeiro]]. The sport grew gradually with 700 amateur players registering within 20 years. Games were played on the beach with modified rules and without the traditional football equipment due to its lack of availability in Brazil. Eventually, a tournament, the Carioca championship, was founded, with the championship [[Carioca Bowl]] played to determine a league champion. The country saw its first full-pad game of football in October 2008.<ref>{{cite web |title=Football in Brazil. Wait, Don't You Mean Soccer?! |url=https://bleacherreport.com/articles/156650-football-in-brazil-wait-dont-you-mean-soccer |website=[[Bleacher Report]] |access-date=August 3, 2019 |date=April 15, 2009 |archive-date=August 3, 2019 |archive-url=https://web.archive.org/web/20190803190634/https://bleacherreport.com/articles/156650-football-in-brazil-wait-dont-you-mean-soccer |url-status=live }}</ref> According to ''[[The Rio Times]]'', the sport is one of the fastest-growing sports in Brazil and is almost as commonly played as soccer on the beaches of Copacabana and [[Botafogo]].<ref name="Rio">{{cite web |last1=Powell |first1=George |last2=Sherman |first2=Blake |title=American Football on the Rise in Rio |url=https://riotimesonline.com/brazil-news/rio-sports/american-football-on-the-rise-in-rio/ |website=[[The Rio Times]] |access-date=August 3, 2019 |date=November 5, 2013 |archive-date=August 3, 2019 |archive-url=https://web.archive.org/web/20190803190646/https://riotimesonline.com/brazil-news/rio-sports/american-football-on-the-rise-in-rio/ |url-status=live }}</ref>

Football in [[Brazil]] is governed by the [[Confederação Brasileira de Futebol Americano]] (CBFA), which had over 5,000 registered players as of November 2013. The sport's increase in popularity has been attributed to games aired on [[ESPN]], which began airing in Brazil in 1992 with Portuguese commentary.<ref>{{cite web |last1=Monsanto |first1=Jayme |title=American Football in Brazil |url=https://riotimesonline.com/brazil-news/rio-sports/american-football-in-brazil/ |website=[[The Rio Times]] |access-date=August 3, 2019 |date=August 4, 2009 |archive-date=October 19, 2010 |archive-url=https://web.archive.org/web/20101019075859/https://riotimesonline.com/brazil-news/rio-sports/american-football-in-brazil/ |url-status=live }}</ref> The popularity and "easy accessibility" of non-contact versions of the sport in Brazil has led to a rise in participation by female players.<ref name="Rio" /> According to ESPN, the American football audience in Brazil increased 800% between 2013 and 2016. The network, along with [[Esporte Interativo]], airs games there on cable television. Football is often associated in Brazil as being the sport of supermodel [[Gisele Bündchen]]'s ex-husband [[Tom Brady]]. The NFL has expressed interest in having games in the country, and the Super Bowl has become a widely watched event in Brazil at bars and [[movie theater]]s.<ref name="Crescimento do interesse por futebol americano no Brasil atrai NFL">{{cite web|last=Macedo|first=Sandro|title=Crescimento do interesse por futebol americano no Brasil atrai NFL|url=http://www1.folha.uol.com.br/esporte/2017/02/1855099-crescimento-do-interesse-por-futebol-americano-no-brasil-atrai-nfl.shtml|work=[[Folha de S.Paulo]]|access-date=April 28, 2017|date=February 2, 2017|archive-url=https://web.archive.org/web/20170525151531/http://www1.folha.uol.com.br/esporte/2017/02/1855099-crescimento-do-interesse-por-futebol-americano-no-brasil-atrai-nfl.shtml|archive-date=May 25, 2017|url-status=live|language=pt}}</ref>

Further countries have also expressed interest in football to lesser degrees. The [[Arab world]] has expressed growing interest in American football, with many countries in the region being members of [[IFAF Asia]]. [[Jordan]] and the [[United Arab Emirates]], which are not members of IFAF, have established their own domestic leagues. [[Egypt]] established two leagues for the sport, namely the Egyptian League of American Football and the [[Egyptian Federation of American Football|Egyptian Federation]] of American Football, and [[Saudi Arabia]] hosts two teams based out of [[Jeddah]] and [[Yanbu]] respectively.<ref>{{Cite web |date=2017-02-03 |title=American Football Gaining Popularity in Arab Countries |url=https://www.americanfootballinternational.com/american-football-gaining-popularity-arab-countries/ |access-date=2023-11-14 |website=American Football International |language=en-US}}</ref><ref>{{Cite web |last=Scb 2019 |date=2023-05-26 |title=The Most Unexpected Countries Where American Football is Played |url=https://steelcityblitz.com/the-most-unexpected-countries-where-american-football-is-played/ |access-date=2023-11-14 |website=Steel City Blitz |language=en-US}}</ref> [[China]] has additionally been a target for the expansion of the sport, with the Mainland being the home of the [[Chinese National Football League]] as well as a growing audience of Super Bowl watchers. Three franchises are also based out of [[Hong Kong]], which prior to the [[COVID-19 pandemic]] regularly played mainland teams. NFL games average 900,000 viewers in China, though the league has cited logistical challenges which would prevent teams from playing games akin to abroad games in European countries.<ref>{{Cite web |date=2022-06-12 |title=American football in Hong Kong is punching above its weight |url=https://www.scmp.com/sport/football/article/3181231/did-you-know-they-play-american-football-hong-kong-no-we-didnt |access-date=2023-11-14 |website=South China Morning Post |language=en}}</ref>

==Variations and related sports==
{{See also|Canadian football|Arena football|Flag football}}
[[File:US Navy 111202-N-FC065-001 Cmdr. Bill Mallory tries for more yards after a reception during a flag football game celebrating the annual Army-Navy f.jpg|thumb|upright=1|alt=Photograph of men playing flag football|Men playing a game of [[flag football]]]]
[[Canadian football]], the predominant form of football in Canada, is closely related to American football—both sports developed from rugby and are considered to be the chief variants of gridiron football.<ref name="Encyclopædia Britannica">{{cite encyclopedia|url=https://www.britannica.com/EBchecked/topic/212839/gridiron-football|title=Gridiron football|pages=1, 13–14|encyclopedia=[[Encyclopædia Britannica Online]]|access-date=January 10, 2013|archive-url=https://web.archive.org/web/20130116191212/https://www.britannica.com/EBchecked/topic/212839/gridiron-football|archive-date=January 16, 2013|url-status=live}}</ref> Although both games share a [[Comparison of American and Canadian football|similar set of rules]], there are several key rule differences: for example, in Canadian football the field measures {{convert|150|by|65|yd|m}}, including two 20-yard end zones (for a distance between goal lines of 110 yards),<ref name="Argos, Rogers Centre agree on lease deal through 2017">{{cite web|title=Argos, Rogers Centre agree on lease deal through 2017|url=http://www.cbc.ca/sports/football/cfl/argos-rogers-centre-agree-on-lease-deal-through-2017-1.1861980|publisher=[[CBC Sports]]|access-date=April 19, 2014|date=September 20, 2013|archive-url=https://web.archive.org/web/20140420224143/http://www.cbc.ca/sports/football/cfl/argos-rogers-centre-agree-on-lease-deal-through-2017-1.1861980|archive-date=April 20, 2014|url-status=live}}</ref> teams have three downs instead of four, there are twelve players on each side instead of eleven,<ref name="Behind IDFFL, Canadian players chase football dreams">{{cite magazine|last=Staples|first=Andy|title=Behind IDFFL, Canadian players chase football dreams|url=http://sportsillustrated.cnn.com/college-football/news/20130628/canadian-football-recruiting/|magazine=[[Sports Illustrated]]|access-date=April 19, 2014|date=June 28, 2013|archive-url=https://web.archive.org/web/20140420041857/http://sportsillustrated.cnn.com/college-football/news/20130628/canadian-football-recruiting/|archive-date=April 20, 2014}}</ref> fair catches are not allowed, and a [[Single (football)|rouge]], worth a single point is scored if the offensive team kicks the ball out of the defense's end zone.<ref name="Head to Head: CFL vs. NFL" /> The Canadian Football League (CFL) is the major Canadian league and is the second-most popular sporting league in Canada, behind the National Hockey League.<ref name="Head to Head: CFL vs. NFL">{{cite web|url=http://www.carillonregina.com/?p=2097|title=Head to Head: CFL vs. NFL|last1=Buchinski|first1=Colin|last2=Neu|first2=Dietrich|date=January 6, 2011|work=[[The Carillon (Regina)|The Carillon]]|access-date=January 10, 2013|archive-date=February 15, 2022|archive-url=https://web.archive.org/web/20220215012503/https://www.carillonregina.com/head-to-head-cfl-vs-nfl/|url-status=live}}</ref> The NFL and CFL had a formal working relationship from 1997 to 2006.<ref>{{cite web |last1=Fitz-Gerald |first1=Sean |title=CFL ends working agreement with NFL |url=http://www.nationalpost.com/ends+working+agreement+with/563856/story.html |website=[[National Post]] |access-date=August 10, 2019 |date=June 4, 2008 |archive-date=February 14, 2022 |archive-url=https://wayback.archive-it.org/all/20220214103133/https://nationalpost.com/ |url-status=live }}</ref> The CFL has a strategic partnership with two American football leagues, the German Football League (GFL) and the Liga de Futbol Americano Profesional (LFA).<ref>{{cite web |title=CFL and GFL form strategic football partnership |url=https://www.cfl.ca/2019/01/31/cfl-gfl-form-strategic-football-partnership/ |publisher=[[Canadian Football League]] |access-date=August 10, 2019 |language=en |date=January 31, 2019 |archive-date=August 10, 2019 |archive-url=https://web.archive.org/web/20190810195416/https://www.cfl.ca/2019/01/31/cfl-gfl-form-strategic-football-partnership/ |url-status=live }}</ref> The Canadian rules were developed separately from the American game.

[[Indoor American football|Indoor football]] leagues constitute what ''[[The New York Times]]'' writer Mike Tanier described as the "most minor of minor leagues." Leagues are unstable, with franchises regularly moving from one league to another or merging with other teams, and teams or entire leagues dissolving completely; games are only attended by a small number of fans, and most players are [[semi-professional]] athletes. The [[Indoor Football League]] is an example of a prominent indoor league.<ref name="Staying in the Game on Football's Fringe">{{cite news|url=https://www.nytimes.com/2011/06/28/sports/football/staying-in-the-game-on-footballs-fringe.html|title=Staying in the Game on Football's Fringe|last=Tainer|first=Mike|date=June 27, 2011|newspaper=[[The New York Times]]|access-date=January 19, 2013|archive-url=https://web.archive.org/web/20120821234055/http://www.nytimes.com/2011/06/28/sports/football/staying-in-the-game-on-footballs-fringe.html|archive-date=August 21, 2012|url-status=live}}</ref> The [[Arena Football League]], which was founded in 1987 and ceased operations in 2019, was one of the longest-lived indoor football leagues.<ref name=GleesonChap7>{{citation |url=https://www.usatoday.com/story/sports/nfl/2019/11/27/arena-football-league-declares-bankruptcy-shuts-down/4322126002/ |title=Arena Football League files for bankruptcy, ceases all operations |last=Gleeson |first=Scott |website=[[USA Today]] |date=November 27, 2019 |access-date=November 27, 2019 |archive-date=November 27, 2019 |archive-url=https://web.archive.org/web/20191127213626/https://www.usatoday.com/story/sports/nfl/2019/11/27/arena-football-league-declares-bankruptcy-shuts-down/4322126002/ |url-status=live }}</ref> In 2004, the league was called "America's fifth major sport" by ''[[ESPN The Magazine]]''.<ref name="Arena football: Is it America's fifth major sport?">{{cite web|url=http://usatoday30.usatoday.com/sports/football/2007-04-13-sw-arena-football_N.htm|title=Arena football: Is it America's fifth major sport?|last=Colston|first=Chris|date=April 15, 2007|work=[[USA Today]]|access-date=January 10, 2013|archive-url=https://web.archive.org/web/20131019122357/http://usatoday30.usatoday.com/sports/football/2007-04-13-sw-arena-football_N.htm|archive-date=October 19, 2013|url-status=live}}</ref>

There are several non-contact variants of football, such as [[flag football]].<ref name="NFL FLAG football is about fun and fundamentals">{{cite web|last=Mills|first=Amy|title=NFL FLAG football is about fun and fundamentals|url=http://usafootball.com/blog/fundamentals-and-performance/nfl-flag-football-about-fun-and-fundamentals|publisher=[[USA Football]]|access-date=April 19, 2014|date=July 30, 2013|archive-url=https://web.archive.org/web/20140420053206/http://usafootball.com/blog/fundamentals-and-performance/nfl-flag-football-about-fun-and-fundamentals|archive-date=April 20, 2014|url-status=live}}</ref> In flag football the ballcarrier is not tackled; instead, defenders aim to pull a flag tied around the ballcarrier's waist.<ref name="Proper flag pull takes fast feet and discipline">{{cite web|last=Musto|first=Adam|title=Proper flag pull takes fast feet and discipline|url=http://usafootball.com/news/coaches/proper-flag-pull-takes-fast-feet-and-discipline|publisher=[[USA Football]]|access-date=April 19, 2014|date=March 19, 2012|archive-url=https://web.archive.org/web/20140420052244/http://usafootball.com/news/coaches/proper-flag-pull-takes-fast-feet-and-discipline|archive-date=April 20, 2014|url-status=live}}</ref> Another variant, [[Touch football (American)|touch football]], simply requires the ballcarrier to be touched to be considered downed. Depending on the rules used, a game of touch football may require the ballcarrier be touched with either one or two hands to be considered downed.<ref name="The 32 Rules of Thanksgiving Touch Football">{{cite news|url=https://www.wsj.com/articles/SB10001424052970204531404577050370294096452|title=The 32 Rules of Thanksgiving Touch Football|last=Gay|first=Jason|work=[[The Wall Street Journal]]|date=November 21, 2011|access-date=January 10, 2013|archive-url=https://web.archive.org/web/20150101014214/http://www.wsj.com/articles/SB10001424052970204531404577050370294096452|archive-date=January 1, 2015|url-status=live}}</ref>

==See also==
{{Portal|American football|Sports}}
{{div col|colwidth=28em}}
* [[American football strategy]]
* [[Comparison of American football and rugby union]]
* [[Comparison of American football and rugby league]]
* [[Fantasy football (gridiron)]]
* [[List of American football films]]
* [[Lists of American football players]]
* [[List of American football stadiums by capacity]]
* [[List of American and Canadian football leagues]]
* [[Doping in American football]]
{{div col end}}

== Notes ==
{{Reflist|group="nb"}}

==Footnotes==
{{Reflist}}

==References==
{{Refbegin}}
* {{cite book | last = Bennett | first = Tom | title = The Pro Style: The Complete Guide to Understanding National Football League Strategy | publisher=National Football League Properties, Inc., Creative Services Division | location = Los Angeles | year = 1976}}
* {{cite web|url=http://refereenation.docs.s3.amazonaws.com/2011_NFHS_Football_Rules.pdf|title=2011 NFHS Football Rules Book|year=2011|publisher=Gardener, Robert B.. [[National Federation of State High School Associations|NFHS Publications]]|editor=Colgate, Bob|url-status=dead|archive-url=https://web.archive.org/web/20160304084406/http://refereenation.docs.s3.amazonaws.com/2011_NFHS_Football_Rules.pdf|archive-date=March 4, 2016}}
* {{cite book|title=Sports Capitalism: The Foreign Business of American Professional Leagues|first=Frank P.|last=Jozsa| publisher=[[Ashgate Publishing]]|year=2004| isbn=978-0-7546-4185-8|url=https://archive.org/details/sportscapitalism0000jozs}}
* {{cite book|last=Nelson|first=David M.|author-link=David M. Nelson|title=The Anatomy of a Game: Football, the Rules, and the Men Who Made the Game|publisher=[[University of Delaware Press]]|date=December 12, 1993|edition=1|page=15|isbn=978-0-87413-455-1|url=https://books.google.com/books?id=OmwfnipKuogC|access-date=August 23, 2020|archive-date=August 19, 2020|archive-url=https://web.archive.org/web/20200819170303/https://books.google.com/books?id=OmwfnipKuogC|url-status=live}}
* {{cite web|url=http://static.nfl.com/static/content/public/image/rulebook/pdfs/2012%20-%20Rule%20Book.pdf|title=Official Playing Rules and Casebook of the National Football League|year=2012|website=[[National Football League]]|access-date=January 14, 2013|archive-date=April 23, 2013|archive-url=https://web.archive.org/web/20130423042036/http://static.nfl.com/static/content/public/image/rulebook/pdfs/2012%20-%20Rule%20Book.pdf|url-status=live}}
* {{cite journal|url=http://www.ncaapublications.com/productdownloads/FR12.pdf|title=NCAA Football Rules and Interpretations|publisher=[[National Collegiate Athletic Association]]|year=2011–2012|last=Redding|first=Rogers|journal=Ncaa Water Polo Rules|editor-last=Halpin|editor-first=Ty|issn=0736-5144|access-date=January 14, 2013|archive-date=August 19, 2013|archive-url=https://web.archive.org/web/20130819102700/http://www.ncaapublications.com/productdownloads/FR12.pdf|url-status=live}}
* {{cite book|title=Sociology of Sport and Social Theory|date=August 11, 2009|isbn=978-0-7360-7572-5|publisher=Human Kinetics|url=https://books.google.com/books?id=Vhbpot6Jk1EC&q=masculinity+football&pg=PA146|editor=Smith, Earl|access-date=October 15, 2020|archive-date=February 15, 2022|archive-url=https://web.archive.org/web/20220215012455/https://books.google.com/books?id=Vhbpot6Jk1EC&q=masculinity+football&pg=PA146|url-status=live}}
* {{cite book | last = Vancil | first = Mark (''Ed.'') | title = ABC Sports College Football All-Time All-America Team | publisher=[[Hachette Books|Hyperion Books]] | location = New York | year = 2000 | isbn = 978-0-7868-6710-3}}
{{Refend}}

== Further reading ==
* ''[https://www.worldcat.org/title/football-great-writing-about-the-national-sport/oclc/895301624/editions Football: Great Writing About the National Sport]'', edited by John Schulian; 2014 (New York: [[Library of America]]; {{isbn|978-1598533071}}).

==External links==
{{Sisterlinks|d=Q41323|wikt=American football|voy=American football|n=Category:Football (American)|mw=no|m=no|species=no|s=Category:American football|v=no}}
{{Spoken Wikipedia|En-American Football-article.ogg|date=July 5, 2014}}
* {{Curlie|Sports/Football/American/}}
* [https://www.nfl.com/ National Football League]
* [https://americanfootball.sport/ International Federation of American Football]
* [http://nfl-360.com/ NFL 360, an introductory website to football rules]
* [https://www.loc.gov/item/mp73006300/ Excerpts of a 1903 football game between the University of Chicago and University of Michigan]

{{International American football}}
{{American football in the United States}}
{{Gridiron football concepts}}
{{Football codes}}
{{Team Sport}}
{{European Football Leagues}}
{{Authority control}}

{{DEFAULTSORT:American Football}}
[[Category:American football| ]]
[[Category:1869 introductions]]
[[Category:American culture]]
[[Category:Ball games]]
[[Category:Gridiron football variants]]
[[Category:Sports originating in the United States]]
[[Category:Team sports]]
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