If a runner tries to avoid a tag and runs more than three feet outside of the base path, the runner is out automatically.
Is the base path the line between the bases?No, the base path is the direct line between the base and the runner at the time when the fielder is trying to tag the runner. The base path is the direct line between the runner and the base to which she is either attempting to advance or retreat at the moment that a defensive player is attempting to tag her. Moreover, the base path may be a long way from the base line. For example, a batter who realizes that the third strike was dropped may start running from near the entrance to the bench.
Does running out of the base path always result in an out?In general, runners may run well outside of the base line. For example, if a runner is advancing more than one base, she is able to run faster by rounding the bases rather than slowing down to cut sharp corners. However, the base path rule applies if a tag play is being made on the runner.
What about first base?There is an additional rule when running to first base. The batter should run in the "runners lane," which is a three-foot wide path on the foul side of the first base line; the lane starts halfway from home plate to first base and runs to the orange (outside) bag at first base. If the batter runs outside of the lane and is hit by a throw or interferes with a fielder's effort to catch a throw at first, the batter will be called out.