being forced OOB

[Tmeup]

I would like to say nice job on this board

I had a situation the other day

Player A gets a rebound near the Base line OOB. As he gets the rebound Player B accidentilly bumps him and Player A falls OOB. If Player B would not have touched Player A he never would of went OOB. But if this contact would of occured in the middle of the lane, no where near the OOB line I would not of made a call. I called a push foul on player B.
In this situation I didnt think that Player A should lose possesion of ball, but I didnt think it ahould be a foul either.

What would you do in this situation?