To keep things in small, easily digestible chunks, every football game is divided into quarters and these quarters are divided into smaller segments whenever the game clock stops. In college and pro football, each quarter lasts 15 minutes; high schools use 12-minute quarters.
After the second quarter comes halftime, which is generally a 15-minute break that gives players time to rest and allows bands and cheerleaders time to perform (it also gives fans time to go get a hot dog). There are often halftime ceremonies in which coaches, players, or alumni are honored.
The game clock doesn’t run continuously throughout those 15- or 12-minute quarters, though. (If it did, when would they show the TV commercials?) The clock stops for the following reasons:
Either team calls a timeout. Teams are allowed three timeouts per half. Consecutive team timeouts can be taken, but the second timeout is reduced from a full minute to 40 seconds.
A quarter ends. The stoppage in time enables teams to change which goal they will defend (they change sides at the end of the first and third quarters).
The quarterback throws an incomplete pass.
The ball carrier goes out of bounds.
A player from either team is injured during a play.
An official signals a penalty by throwing a flag.
The officials need to measure whether the offense has gained a first down or need to take time to spot, or place, the ball correctly on the field.
Either team scores a touchdown, field goal, or safety.
The ball changes possession via a kickoff, a punt, a turnover, or a team failing to have advanced the ball 10 yards in 4 downs.
The offense gains a first down (college and high school only).
Two minutes remain in the period (NFL only).
A coach has challenged a referee’s call, and the referees are reviewing the call (NFL only).
Unlike college and professional basketball, where a shot clock determines how long the offense can keep possession of the ball, in football the offense can keep the ball as long as it keeps making first downs.
However, the offense has 40 seconds from the end of a given play, or a 25-second interval after official stoppages (such as replacing a wet ball with a dry one), to get in the proper position after an extremely long pass gain. If the offense doesn’t snap the ball in that allotted time, it’s penalized 5 yards and must repeat the down.
With the exception of the last 2 minutes of the first half and the last 5 minutes of the second half of an NFL game, the game clock is restarted after a kickoff return, after a player goes out of bounds on a play, or after a declined penalty.
