Every half begins with a center jump. The defensive team initiates play by tossing the ball in bounds from behind their own end line. On offense, one player is chosen to be "it" - the player who gets the ball is automatically given two options: keep the ball or hand it off. If the player keeps the ball, they have two choices: stay in or go around. If they go around, they can look for an open teammate or try to run themselves. There are three ways that a half can end: a goal, safety, or foul. If the defensive team stops any attempt at a goal-line stand, then there is no time left on the clock and the game ends in a safety. If the offensive team manages to move the ball downfield into field-goal range, then they get another chance after the defense kicks off to them. If they fail to score, then the other team wins! The first half of every game is played under normal circumstances. The second half of the game involves substitutions - players are replaced by others who come onto the field during these breaks. The term "half" as used in football refers to one period of play of approximately five minutes long.