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.
Mercy rule
The National Collegiate Athletic Association's mercy rule provides, "Any time during the game, the playing time of any remaining period or periods and the intermission between halves may be shortened by mutual agreement of the opposing head coaches and the referee." (NCAA Football Rule 3-2-2-a) NCAA Football Approved Ruling 3-2-2-I cites an example: "At halftime the score is 56–0. The coaches and the referee agree that the third and fourth quarters should be shortened to 12 minutes each. The coaches also request that the second half be played with a 'running clock' i.e., that the game clock not be stopped." The NCAA Football Rules Committee determined, "The remaining quarters may be shortened to 12 minutes each. However, the 'running clock' is not allowed; normal clock rules apply for the entire game."