In what situation is blocking the base while in possession of the ball legal?

Blocking the base while in possession of the ball is a situation that is not permitted under most baseball and softball rules. An exception exists when the defensive player is making a play on a runner, which does not fall under the provided options. In essence, if a defensive player is blocking the base while holding the ball and not making a legitimate attempt to tag the runner during a play, it could interfere with the runner's ability to reach the base safely.

The correct answer indicates that there are no circumstances under which blocking the base while in possession of the ball is legal, aligning with the rules that protect the runner's right to access the base. This serves to maintain fairness in the game, ensuring that players have an unobstructed opportunity to run the bases.