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.
Quarterback
As late as the 1960s, running plays occurred more frequently than passes. NFL quarterback Milt Plum later stated that during his career (1957-1969) passes typically only occurred on third downs and sometimes on first downs. Quarterbacks only increased in importance as rules changed to favor passing and higher scoring and as football gained popularity on television after the 1958 NFL Championship Game, often referred to as "The Greatest Game Ever Played". Early modern offenses evolved around the quarterback as a passing threat, boosted by rules changes in 1978 and 1979 that made it a penalty for defensive backs to interfere with receivers downfield and allowed offensive linemen to pass-block using their arms and open hands; the rules had limited them to blocking with their hands held to their chests. Average passing yards per game rose from 283.3 in 1977 to 408.7 in 1979.
The NFL continues to be a pass-heavy league, in part due to further rule changes that prescribed harsher penalties for hitting the quarterback and for hitting defenseless receivers as they awaited passes. Passing in wide-open offenses has also been an emphasis at the high school and college levels, and professional coaches have devised schemes to fit the talents of new generations of quarterbacks.