American football
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. High school football games are 48 minutes in length with two-halves of 24 minutes and four-quarters of 12 minutes. The two-halves are separated by a halftime period, and the first and third quarters are also followed by a short break. Prior to the start of the game, the referee and team captains for each team meet at midfield for a coin toss. The visiting team is allowed to call 'heads' or 'tails'; the winner of the toss is allowed to decide between choosing whether to receive or kick off the ball or choosing which goal they want to defend, but they can also defer their choice until the second half. The losing team, unless the winning team decides to defer, is allowed to choose the option the winning team did not select, and receives the option 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 would allow the other team to choose which goal to defend. Teams switch goals following the first and third quarters. If a down is in progress when a quarter ends, play continues until the down is completed.
List of gridiron football rules
Scoring and game timing are much different in touch football than its more organized counterpart. For the sake of simplicity, touchdowns are usually worth 1 point and no other scoring is counted (there are no extra point attempts). In a much lesser used variation, a touchdown is worth 6 points and if the player who scored the touchdown can progress in the other direction from the end zone in which he had just scored back to the opposite end zone without being touched, it counts as a two-point conversion. The former scoring method does not allow for other scoring types such as safeties. There is usually no game clock and the game ends when one opponent has reached 10 touchdowns (in the former convention) or 100 points (in a standard convention).The NFL adopted many ideas introduced by the AFL, including names on player jerseys and revenue sharing of gate and television receipts. The older league also adopted the practice of using the stadium scoreboard clocks to keep track of the official game time, instead of just having a stopwatch used by the referee. The AFL played a 14-game schedule for its entire existence, starting in 1960. The NFL, which had played a 12-game schedule since 1947, changed to a 14-game schedule in 1961, a year after the American Football League instituted it; it has been 16-game seasons since 1978. The AFL also introduced the two-point conversion to professional football thirty-four years before the NFL instituted it in 1994 (college football had adopted the two-point conversion in the late 1950s). All of these innovations pioneered by the AFL, including its more exciting style of play and colorful uniforms, have essentially made today's pro football more like the "AFL" than like the old-line NFL. The AFL's challenge to the NFL also laid the groundwork for the Super Bowl, which has become the standard for championship contests in the United States.