Shot goes up by A1, B1 is in postion to rebound blocking out A2, A3 comes flying in over A2,A3's contact with A2 knocks both A2 and B1 out of the play. Foul??? on A3? A2?

I would call foul on A2, A3's contact with A2 is nothing, but since B was displaced and put at a disadvantage, it must be a foul. Since A2 was the contact with B he gets the foul.

TwoDot's explanation is right. If A2 is the only opponent of B1 who makes contact, the foul is on A2. However, the original question is: What do you have? I will confess that I will look very, very carefully at A3 so that *any* contact with B1 will be the contact I will call a foul. Nobody in the gym will be disappointed with a foul call on A3 since it was A3's conduct which violated the spirit of the rules.

There is no way you can ever call a personal foul because the player hit a team-mate. Unless you can find some form of direct contact between A3 and B1 you've got to call the foul on B2.

I seem to remember a case play or interpretation in which the ruling was a personal foul even when there was not contact. The play, as I remember it,.... A1 holding the ball is guarded by B1. B1, using the ball, pushes B1 out of the way.

If I'm remembering this correctly, there is a ruling where a player can be called for fouling another player without having actually made direct contact....but having violated the spirit of the rule.

Given that, it would not be too far fetched to call a foul on player A3 for fouling player B1.