American football (known simply as football in the United States, and gridiron in some other countries) is a sport played by two teams of eleven players on a rectangular field 120 yards long by 53.3 yards wide with goalposts at each end. The offense attempts to advance an oval ball down the field by running with or passing it. They must advance it at least ten yards in four downs to receive a new set of four downs and continue the drive; if not, they turn over the ball to the opposing team. Points are scored by advancing the ball into the end zone for a touchdown, kicking the ball through the opponent's goalposts for a field goal or by the defense tackling the ball carrier in the offense's end zone for a safety.
Early history American football evolved from the sport of rugby football. The first football game was played on November 6, 1869 between Rutgers and Princeton. The game was played between two teams of 25 players each, used a round ball, and resembled a combination of rugby and soccer in its rules. The ball could not be picked up or carried, but it could be kicked or batted with the feet, hands, head or sides. Collegiate play continued for several years in which matches were played using the rules of the host school. Representatives of Yale, Columbia, Princeton and Rutgers met on October 19, 1873 to create a standard set of rules. Teams were set at 20 players each, and fields of 400 by 250 feet were specified. Harvard abstained from the conference, as they favored a rugby-style game that allowed running with the ball.
An 1875 Harvard-Yale game played under rugby-style rules was observed by two impressed Princeton athletes. These players introduced the sport to Princeton, a feat the Professional Football Researchers Association compared to "selling refrigerators to Eskimos." Princeton, Harvard, Yale and Columbia then agreed to intercollegiate play using a form of rugby union rules with a modified scoring system. 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," passed rule changes in 1880 that reduced the team size from 15 to 11 players and instituted the snap to replace the chaotic and inconsistent scrum. Evolution of the game The introduction of the snap resulted in unexpected strategy changes. Previously, the strategy had been to punt if a scrum resulted in bad field position. A group of Princeton players realized that, as the snap was uncontested, they now could hold the ball indefinitely to prevent their opponent from scoring. In 1881, both contestants in a Yale-Princeton game used this strategy to maintain their undefeated records. Each team held the ball, gaining no yardage, for an entire half. This "block game" proved extremely unpopular with spectators and fans.
A rule change was necessary to prevent this, and a reversion to the scrum was considered until Camp passed a rule in 1882 that stated that a team would have three downs, or tackles, to advance the ball five yards. Failure to do so would forfeit control of the ball to the other team. This change made American football a separate sport from rugby, and the resulting five-yard lines added to the field made it resemble a gridiron in appearance. Other major rules changes included a reduction of the field size, to 110 yards long by 53.3 yards wide, and the adoption of a scoring system that awarded four points for a touchdown, two for a safety and a goal following a touchdown, and five for a goal from field. The last major remnant of rugby was removed in 1888, when tackling below the waist was legalized. Football remained a violent sport despite these innovations. Dangerous mass-formations like the flying wedge resulted in serious injuries and even death. A 1905 peak of 19 fatalities nationwide resulted in PresidentTheodore Roosevelt's threat to abolish the game unless major changes were made. Sixty-two schools 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 named the National Collegiate Athletic Association (NCAA).
The legal forward pass was introduced in 1906 after its suggestion by John Heisman, although its impact was limited due to the restrictions placed on its use. Further 1906 rules changes included the reduction of the time of play from 70 to 60 minutes and the increase of the distance requirement for a first down to 10 yards over three downs. Additionally, the neutral zone was created along the width of the football. Field goals were lowered to three points in 1909 and touchdowns raised to six points in 1912.The field was also reduced to 100 yards long, but two 10-yard-long end zones were created, and teams were given four downs instead of three to advance the ball 10 yards. 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.