Line drive right at the 3rd base coach. Coach catches the ball. No fielders are moving to make a play. Is the batter out?
The coach should not be interfering with the ball, period. If is it accidental (or unavoidable) that's different but intentional interfering by a base coach should be called an out - otherwise I could run around the field and distract the opposing team while my girls are up to bat.
I would only stop ground balls hit towards me that were obvious fouls. Speeds up the game when you don't have the girls playing chase to get the errant balls. Fly balls...NEVER. I gave their fielders a clear path to the ball.