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
A standard football game consists of four 15-minute quarters (12-minute quarters in high-school football and often shorter at lower levels, usually one minute per grade [e.g. 9-minute quarters for freshman games]), with a 12-minute half-time intermission (30 minutes in Super Bowl) after the second quarter in the NFL (college halftimes are 20 minutes; in high school the interval is 15 or 20 minutes; 10 minutes for lower grades). 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, timed like the fourth quarter, lasting up to 10 minutes. There is a coin toss in the NFL just like the beginning of the game. If the receiving team scores a touchdown during the possession, they win. If they kick a field goal, then the other team gets a possession. If they score a touchdown, they win. If they tie the score by kicking a field goal, then the next team that scores wins. If the team with the first possession turns the ball over without scoring any points, then the first team to score, wins. If the defense scores a touchdown through an interception or fumble recovery, or they get a safety, then they win. In a regular-season NFL game, if no one scores in the overtime, the game ends tied. In an NFL playoff game, multiple 15-minute overtime periods are played, as needed, to determine a winner. These periods are timed as if a game had started over. In the extremely rare case a game would go as far as a third OT—which has never happened in the NFL—there would be no "halftime intermission"; play would resume with a kickoff similar to a normal third quarter.