hitting on arms during rebound

[ysong]

when both A1 and B1 go for rebound, if A1 grabs the ball with on hand but before A1 is able to secure it with 2 hands, B1, while also goes for the ball, hit A1's arm (accidentally or not) and A1 lose the ball. Is this contact legal in the following scenarios:

1. A1's arm is in his vertical plane.
2. A1's arm is in B1's vertical plane.
3. A1's arm is in neither. (Nor B1's arm).

Alos are there any ruling differences in NCAA, NBA and FIBA?

Thanks for your help to clarify this for me.

ysong