How to Follow the American Football Game Clock

By Howie Long and John Czarnecki from Football For Dummies, 4th US Edition

In an American football game, the game clock, which is operated by a timekeeper in the press box, doesn’t run continuously throughout the game’s 15-minute (for professional or college games) or 12-minute (for high school games) quarters. The clock stops for the following reasons:

Either team calls a timeout. Teams are allowed three timeouts per half.
A quarter ends. The stoppage in time enables teams to change which goal they’ll 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 they 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 advance the ball 10 yards in four downs.
The offense gains a first down (in college and high school only).
Two minutes remain in the half or in overtime (in the NFL only).
A coach has challenged a referee’s call, and the referees are reviewing the call (in college and the NFL only).
A wet ball needs to be replaced with a dry one.

With the exception of the last two minutes of the first half and the last five minutes of the second half of an NFL game, the officials restart the game clock after a kickoff return, after a player goes out of bounds on a play, or after a declined penalty.

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, to get in proper position after an extremely long gain. If the offense doesn’t snap the ball in that allotted time, it’s penalized 5 yards and must repeat the down.