Gridiron football
Play of the game
American football is the most common and widely known of these sports. It was originally more closely related to rugby, until various rule changes created by Walter Camp were implemented in 1880, and the two sports diverged irreversibly after the forward pass was introduced to the American game in 1906. It is played with eleven players to a side, four downs and a 100-yard (91 m) field. The major professional league, the National Football League (NFL), has its own rule book. College football programs generally play under the code defined in the NCAA Football Rules and Interpretations. High schools generally follow the rules and interpretations published by the National Federation of High School Associations (NFHS), although some states follow the NCAA code for high school play. Youth games (below high school age) generally follow NFHS code with modifications. Adult semi-pro, alternative and minor professional, amateur, touch, flag, etc. may follow any one of these codes or use their own rules. While the vast majority of the game is the same among these three codes, subtle variations in rules can lead to large differences in play. Many of the differences are in penalty enforcement and the definitions of fouls. Canadian football is played almost exclusively in Canada. Like its American cousin, it was originally more closely related to rugby, until the Burnside rules were adopted in 1903 (as such, despite their similarities, the modern American and Canadian forms of football were developed separately from each other); the forward pass was adopted in Canada in 1929. The game is played on a 110-yard (100 m) field and has three downs and twelve players to a side. The Canadian game also features a one-point "single" (formally called a "rouge") for a ball kicked into the end zone and not returned by the receiving team. Like the American game, the Canadian Football League and U Sports both have their own rulebooks, although there are generally fewer differences than between their American counterparts, despite some major changes in contrast to its American cousin.[clarification needed] Nine-man football, eight-man football and six-man football are varieties of gridiron football played with fewer players. They are played with the same number of downs (often with a 15-yard [14 m] requirement for a new set of downs, as opposed to 10 in other codes), fewer offensive linemen, and an 80-yard (73 m) field. These games are generally based on the high school rulebooks, which have an addendum devoted to the play of these codes, and are generally played by teams from high schools with very small student bodies, usually in rural areas of the United States. Similar small-roster versions of Canadian football are played in rural Canada. Indoor football is played with special rules to accommodate smaller indoor facilities, usually sharing arenas with basketball or ice hockey teams. It is played on a 50-yard (46 m) field with, usually, eight players to a side. Prototype games were played in 1902 and 1932, both of which used the shortened field but followed the outdoor standard 11 to a side. However, indoor football did not gain popularity until James F. Foster's proprietary version, arena football, debuted in 1986, and set most of the standards for indoor leagues today. As almost all indoor leagues are for-profit professional leagues, each league has its own proprietary code. Sprint football (or lightweight football) is a variant of American football with nearly identical rules but with added restrictions on the maximum weight and percent body fat of players on the field, emphasizing speed and agility over raw size at all positions. It is played at a small number of colleges and universities, mostly in the northeastern United States. Touch football, flag football, wheelchair football, and backyard football are informal varieties of the game, played primarily at an amateur and recreational level. No specific rulebooks are universally recognized for these variants, where house rules usually apply. Women's American football is the organized play of the sport by women. Most organized leagues play by rules identical to standard, male-dominated leagues. The former Lingerie Football League (later the Legends Football League and Extreme Football League) earned a notoriety for its indoor, seven-on-seven variety of women's football with minimal protective equipment and uniforms resembling women's underwear. Female versions of the informal varieties, such as Powderpuff, also exist. Given the popularity of gridiron football in North America yet the rarity of female-only teams at the high school level and above, female players have also played on men's teams on rare occasion. This is a minimal description of the game in general, with elements common to all or almost all variants of the game. For more specific rules, see each code's individual articles.
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