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
In some states (where 8-man and 6-man football is widely used), the rules call for a game to end when one team is ahead by a certain score (like 45 or 50 points) at halftime or any time thereafter. In other states with 6- or 8-man football, continuous clock rules are used, and the rule may be modified; for instance, in Iowa, the rule goes into effect if the 35-point differential is reached at any time after the first quarter.