<P> In baseball, a runner must sometimes advance to the next base because a batter, advancing to first, forces that runner to advance ahead of him to the next base . Two runners are not allowed on one base at one time, so a batter can, in effect, bumper - car a runner forward . Such a runner is spoken of as having been forced to the next base . A defensive play against that runner is called a force play and, if successful, a force out . A tag can put runners out on a forced play as well (in lieu of stepping on a force base). </P> <P> 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 . </P> <P> Tag plays can also be utilized in other cases when the runner is in jeopardy . A baserunner is in jeopardy when: </P> <Ol> <Li> he is not touching a base (excluding overrunning of first base or when advancing to an awarded base, such as on a base on balls); </Li> <Li> he is touching a base he has been forced to vacate because the batter became a baserunner (a forced runner) </Li> <Li> he has not tagged up on a caught fly ball; </Li> <Li> he failed to touch a base when he last passed it, or to touch them in order; or </Li> <Li> he is touching a base that a preceding baserunner is also touching, except when forced to vacate the previous base because the batter became a baserunner </Li> </Ol>

When do you have to tag a runner