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.
NFL preseason
The exhibition season typically begins the first weekend of August with the Hall of Fame Game; though in some years it can be on the second weekend. Previous seasons have seen the American Bowl game held the last weekend of July. The first full schedule of exhibition games is held the following weekend. Most games are held on Thursday, Friday, or Saturday nights, with one nationally televised game each night of the week: NFL Network airs a Thursday game, CBS and Fox a Friday and Saturday night game each, NBC with Sunday night games, and ESPN a Monday night game. Unlike the regular season, CBS's and Fox's national exhibition game opponents are selected regardless of conference. Four full weekends of games are held. The fourth and final full week of exhibition games (fifth weekend overall) usually has teams playing exclusively on Thursday night (plus Friday, if any), with no national games. This allows teams a few extra days to prepare for the first week of the regular season. It also prevents conflict with the start of the regular seasons for high school and college football, allowing those venues to expand their first weekends' games from Thursday through Monday (Labor Day).