Force play

In baseball, a force is a situation when a baserunner is compelled (or forced) to vacate his time-of-pitch base—and thus try to advance to the next base—because the batter became a runner. A runner at first base is always forced to attempt to advance to second base when the batter becomes a runner. Runners at second or third base are forced only when all bases preceding their time-of-pitch base are occupied by other baserunners and the batter becomes a runner.

A forced runner's force base is the next base beyond his time-of-pitch base. Any attempt by fielders to put a forced runner out is called a force play. Think of forced runners as bumper cars. If with a runner on first, the batter hits a ground ball, the batter must run to first, and since two runners are not allowed to stay on one base at one time, the runner who was on first to begin with is now bumper-carred by the advancing batter over to second. If there already was a runner on second as well, that runner is now bumper-carred over to third, and so on. If a runner is bumper-carred over to the next base by the advancing batter or by another runner who was bumper-carred by the advancing batter, then that runner is considered to have been forced to advance to the next base. If, however, with a runner on third, for example, the batter hits a ground ball, the batter must run to first, but the runner on third, not having been bumper-carred by the batter, is not forced to advance and can stay where he is if he elects to.