American football, known in the United States and Canada simply as football,[1] is a competitive team sport known for mixing strategy with physical play. The objective of the game is to score points by advancing the ball[2] into the opposing team's end zone. The ball can be advanced by carrying it (a running play) or by throwing it to a teammate (a passing play). Points can be scored in a variety of ways, including carrying the ball over the opponent's goal line; catching a pass from beyond that goal line; kicking the ball through the goal posts at the opponent's end zone; and tackling an opposing ballcarrier within his end zone. The winner is the team with the most points when the time expires.
The sport is also played outside the United States. National leagues exist in Germany, Italy, Switzerland, Finland, Sweden, Japan, Mexico, Israel, Spain, Austria and several Pacific Island nations. The National Football League, the largest professional American football league in the world, ran a developmental league in Europe from 19911992 and then from 19952006.
American football is closely related to Canadian football. Both sports originated from rugby football.
The history of American football can be traced to early versions of rugby football and soccer. Both games have their origins in varieties of football played in the United Kingdom in the mid-19th century, in which a ball is kicked at a goal and/or run over a line. Also like soccer, American football has twenty two players on the field of play. Furthermore, some player position references from soccer are used, such as the term "halfback" and "fullback".
American football is played on a field 360 by 160 feet (109.7 m 48.8 m). The longer boundary lines are sidelines, while the shorter boundary lines are end lines. Near each end of the field is a goal line; they are 100 yards (91.4 m) apart. A scoring area called an end zone extends 10 yards (9.1 m) beyond each goal line to each end line. While the playing field is effectively flat, it is common for a field to be built with a slight crownwith the middle of the field higher than the sidesto allow water to drain from the field.
Yard lines cross the field every 5 yards (4.6 m), and are numbered every 10 yards from each goal line to the 50-yard line, or midfield (similar to a typical rugby league field). Two rows of short lines, known as inbounds lines or hash marks, run parallel to the sidelines near the middle of the field. All plays start with the ball on or between the hash marks.
At the back of each end zone are two goalposts (also called uprights) connected by a crossbar 10 feet (3.05 m) from the ground. The posts are, for high skill levels 222 inches (5.64 m) apart. For lower skill levels, these are widened to 280 inches (7.11 m).
Each team has 11 players on the field at a time. However, teams may substitute for any or all of their players, if time allows, during the break between plays. As a result, players have very specialized roles, and, sometimes (although rarely) almost all of the (at least) 46 active players on an NFL team will play in any given game. Thus, teams are divided into three separate units: the offense, the defense and the special teams.
A standard football game consists of four 15-minute quarters (12-minute quarters in high-school football and often shorter at lower levels), with a half-time intermission after the second quarter. The clock stops after certain plays; therefore, a game can last considerably longer (often more than three hours in real time), and if a game is broadcast on television, TV timeouts are taken at certain intervals of the game to broadcast commercials outside of game action. If an NFL game is tied after four quarters, the teams play an additional period lasting up to 15 minutes. In an NFL overtime game, the first team that scores wins, even if the other team does not get a possession; this is referred to as sudden death. In a regular-season NFL game, if neither team scores in overtime, the game is a tie. In an NFL playoff game, additional overtime periods are played, as needed, to determine a winner.