Batter interference on runner scoring from third

[rinbee]

I umpire LL Minor Division and I have heard two interpretations of the batter interference call when a runner is attempting to score from third. Which is correct:

a) It is batter interference when the batter fails to leave the box regardless of whether the defensive team is makaing a play on the runner attempting to score

b) It is only batter interference if the batter remains in the box and -- in the umpire's judgment -- the defense was in the act of making a play on the runner. I believe this is the correct interpretation because it is consistent with the case of a batter-runner beign inside the baseline going to first adn is only guilty of interference when a play is actually attempted.