Comparison of American football and rugby union
A rugby union game is divided into two halves of 40 minutes (or shorter for lower-grade games, and breaks given halfway through each half if playing conditions are considered to be extreme) separated by a half time period of up to 15 minutes in an international match. Most notably, a rugby union game will continue after the scheduled end of a half (half-time or full-time) until the ball becomes dead - any occurrence that would have play restart with a scrum or lineout, or when a team scores. This has led to some "nail-biting" finishes where teams losing by only a small margin work their way towards scoring, and games can go on several minutes over time. Something similar can occur at the end of either half in American football, though usually for only a few seconds of additional time, because a play that begins before the half expires continues until the ball is dead regardless of whether there is any time left on the clock. In both sports, the clock is also stopped during substitutions and for injuries, so the referee does not need to add stoppage time as is done in soccer/Association football. American football games are made up of four quarters of 15 minutes each (less at the high school and youth levels), but the clock stops and starts according to specific rules, so that a 15-minute quarter lasts much longer.
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.