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.
College soccer
While similar in general appearance, NCAA rules diverge significantly from FIFA Laws of the Game. A manager may make limited substitutions, and each player is allowed one re-entry which must occur in the second half of the match unless the substitution was caused by a player injury resulting from a caution or send-off. All matches have an overtime period if the game remains tied after 90 minutes. As opposed to a regular two-half extra time period, golden goal is applied. If neither team scores in the two ten-minute periods, the match ends in a draw (unless it is a playoff match, then it would go to a penalty shootout). College soccer is played with a clock that can be stopped when signaled to by the referee for injuries, the issuing of cards, or when the referee believes a team is wasting time. The clock is also stopped after goals until play is restarted, and the clock generally counts down from 45:00 to 0:00 in each half. In most professional soccer leagues, there is an up-counting clock with the referee adding stoppage time to the end of each 45-minute half.