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.
Time on
Time on was first introduced to the Laws of the Game by the Australian National Football Council for the 1928 season. From 1928 until 1994, quarters lasted 25 minutes playing time, and time on was called only for scores and injuries; the rule of thumb was that there would be roughly one minute of time-on for every goal scored. From 1994, the AFL Commission adopted the shorter 20 minute quarter, and introduced time-on for many other stoppages, including a ball-up or boundary throw-in.