In baseball, a force play or force out occurs when a runner is required to advance to a base which a player on the opposing team has already reached while in possession of the ball.
There are two situations in which a force play occurs: One, a batter becomes a runner and gets put out because an opponent with possession of the ball reaches first base before the batter can get there.
For example, with a runner on first, the batter hits a ground ball to the second baseman.
This most often happens on fly outs—on such, the batter-runner is out, and the other runner(s) must return to their time-of-pitch base, known as tagging up.
It also occasionally happens when a sharply hit ground ball is fielded by the first baseman, who then quickly steps on first base to put out the batter-runner.
As a result, on a batted ball with two outs, fielders will nearly always ignore a runner trying to score, attempting instead to force out the batter or another runner.
An appeal play may also be a force play; for example, with runners on first and third bases and two out, the batter gets a hit but the runner from first misses second base on the way to third.
But it is not, which means the run would count if it scored before the third out is made on a different runner trying to tag up.