- The stadium game clock is the official method of timing for a game. If the game clock should somehow stop or appear to be malfunctioning, the official to whom the task of timekeeping passes is the Line Judge.
- Each period, or quarter, lasts 15 minutes, or a quarter of an hour. There is also a two-minute intermission between the first and second and the third and fourth quarters. Halftime is supposed to last for 12 minutes, but may last longer if specified ahead of time in order to accommodate a special program or promotion.
- Charged team time outs usually last for one minute and 50 seconds, although the amount of time may be reduced to 40 seconds if the network televising the game does not use the time out to air a commercial. Each team is given three time outs per half, and while opposing teams may take consecutive time outs if they so choose, the second time out will only be 40 seconds in length. A defensive team may actually lose time outs, due to a penalty imposed if the referee judges that the level of crowd noise is preventing the offense from hearing signals.
- The time clock is stopped between plays for 40 seconds from the end of the play until the ball is snapped for the next one.The game clock is restarted following a kickoff return, when a player goes out of bounds on a scrimmage play, or when penalties are declined on a signal from the referee. The clock starts running as soon as the ball is snapped after a change in possession. The clock may also be stopped for 25 seconds, due to certain types of administrative delay.
- If a player is injured, the clock may be stopped for as long as is necessary to attend to the injury. The clock may also be stopped if a player is uninjured, but his equipment becomes detached or damaged. In this case, the clock will be stopped for such time as is needed to make the needed repairs.
