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.
Official (American football)
In high school and minor leagues, the line judge is the official timekeeper of the game. In the NFL, college, and other levels of football, the official time is instead kept on the stadium scoreboard clock, and the line judge becomes the backup timekeeper.