In baseball, a force play or force out, referred to as a force when the possibility of such a play exists, is a situation when a baserunner is compelled to vacate his time-of-pitch base because the batter became a runner. This occurs if all bases preceding the baserunner's time-of-pitch base were occupied; for example, a runner at first base is always forced to attempt to advance to second base when the batter becomes a runner.

A runner may be put out when a fielder with the ball touches the base to which the forced runner is advancing. The runner also may be tagged out in the usual fashion as well; this tag is still considered a force play. Any play on the batter-runner before he reaches first base is considered the same as a force play, though the rules technically do not include this in the definition.

No run can be scored during the same continuous playing action as a force out for the third out, even if a runner reaches home plate before the third out is recorded. 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, suppose the batter gets a hit but the runner from first misses second on the way to third. After a proper appeal, this runner will be called out. This is a force out and thus the run does not count.

A runner's force base is the next base after his time-of-pitch base, if all bases preceding the runner's time-of-pitch position were occupied at the time of pitch.