Force play
In baseball, any player from the team that is trying to score who is on one of the bases (a runner) can not be safe on that base anymore if there is another player from their team who has become unsafe at the previous base in the same way; the runner is then said to be forced to run. The batter can be considered as no longer being safe at home base (which can be thought of as the base that comes "before" first base) when he has hit the ball into the fair part of the field. A forceout occurs when a player on the fielding team touches a base while holding the ball and a runner at the previous base was made unsafe in this way; that runner is then out.