Is it ever legal to slap the ball out of an inbounders hands?

[thereluctantref]

Is it legal for a defender to slap the ball out of the hands of an inbounder if the ball breaks the imaginary out of bounds line plane? This happened last season when I was refereeing and I was looking for a definitive answer but didn't get one online. My partner and I gave a warning to the defender who slapped the ball out of the inbounder's hands and then gave a technical when she did it again. The coach argued and asked us if it were okay to hit the ball away if the ball broke the plane of the out of bounds line. We said it was never okay but then I read about it later and had second thoughts...(when I reflected about this situation, the point was moot because the inbounder didn't let the ball break the plane; I think the coach was just trying to give us a hard time...)