A batter can also advance to the next base because he chooses to. For example, suppose, with a runner on first, the batter hits a groundball single into the outfield. As the batter runs to first, the runner on first is forced to advance ahead of him to second. However, that runner can then choose to run past second and on to third. In this situation, a defensive play against such an unforced runner will be called a tag play and, if successful, a tag out. To get the runner out on a tag play, the fielder must tag him with the ball before the runner gets to the targeted base. Tag plays are much more difficult to execute than force plays.
when does a runner have to be tagged in baseball
To get the runner out on a tag play