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.
Timewasting
In American Football, teams leading late in the game will often make low-risk rushing plays to keep the game clock counting down, as the clock stops on an incomplete pass or a run out of bounds. This can also force the trailing team to use up their timeouts. If the opposing team has no timeouts, a leading team needs to make one first down after the two-minute warning. The quarterback will then "take a knee" on three consecutive plays, wasting 40 seconds each time, to allow the clock to run out.