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.
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.