Under what condition can a base runner be called out for interfering with a fielder?

A base runner can be called out for interfering with a fielder if the runner fails to avoid the fielder, regardless of whether the fielder has possession of the ball or not. This rule is designed to ensure that base runners do not impede the ability of fielders to play the ball and make defensive plays. The spirit of this rule is to maintain fair play and to prevent collisions that could result in injury or unfair advantages during the game.

When a runner collides with a fielder or obstructs their path, it can be seen as an attempt to disrupt the defense's ability to make a play, which warrants the interference call, even if the fielder does not have the ball. The emphasis is on the runner's responsibility to avoid contact with a fielder who is in a position to make a play, creating a clear standard for what constitutes interference within the game.