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
At the middle- or high-school level, 34 states use a mercy rule that may involve a "continuous clock" (the clock continues to operate on most plays when the clock would normally stop, such as an incomplete pass) once a team has a certain lead (for example, 35 points) during the second half. That greatly decreases the amount of time taken for a game to complete, which reduces the leading team's chances to score more and the time that the trailing team must spend in facing an insurmountable deficit. In most states, the clock stops only for scores, timeouts (officials', injury, or charged), or the end of the quarter. Plays that would normally stop the clock, such as penalties, incomplete passes, going out of bounds, or change of possession, would not stop the clock. The rule varies by state; for example, the clock does not stop upon a score in Colorado, Kansas (regular-season games only), or Missouri (fourth quarter only).