Force Outs/Force Plays
Example For Out Situation
For example, if a batter hits a ground ball and there is a runner on first base, that runner must advance because the batter-runner is approaching first base, and they cannot occupy that base at the same time.
Stepping On The Bag
If the second baseman has fielded the baseball, he can simply step on second base before the runner (who was previously on first base) reaches it, and that runner is out. Since the original runner was forced off his previous base to advance to a base that had just been tagged by a fielder, that runner is considered to be forced out.
Sometimes, batter-runners reach first base on what is called a fielder's choice. This occurs when there is a runner already on base, the batter hits a ground ball, and the fielders decide to put out the pre-existing runner at his next base rather than the batter-runner. Therefore, the batter-runner reaches first base safely.