The last two minutes of a half can take a long time to play. Throughout the game, the clock is stopped whenever there is an incomplete pass or the player with the ball runs out-of-bounds. And the clock is stopped temporarily when there's a first down so the officials can move the chains at the side of the field that are used to measure the 10 yards. And each team has 3 time-outs they can call per half to stop play for a couple of minutes. In the last 2 minutes, the offense uses incomplete passes and running out-of-bounds just to stop the clock. Unlike professional football, there is no "two minute warning."