Running out the clock
In American football, each quarter of a game is measured with a 15-minute game clock, or 12-minute clock in many high school football codes and the German Football League. A team in possession of the lead and the ball will attempt to use up as much of the game clock as possible in order to bring the game to an end more quickly, thus denying the opposition another chance on offense.
American football rules
If a game goes to overtime, a coin toss is held before the start of overtime, but tosses are not held before the start of subsequent overtime periods. In college, for example, the loser of the toss to start overtime has first choice in the second overtime period. The choices available to the captains in overtime vary among the NFL, college, and various states' high school rules.