[ChuckElias]

Ok, so A1 shoots while jumping forward slightly. Once the shot is away, B1 turns to face the basket. A1 lands on B1's heels.

The question here is whether B1 moved out of his vertical space (toward A1) while A1 was in the air. If B1 simply turned around, then you've got nothing. B1 is entitled to be there, since he was legally there before A1 went airborne.

If B1 turned around and then started to back up, then you might consider a foul on B1. Without seeing the contact and the fall (might there have been some acting to attract your attention?), I can't say if it should be a foul or not. But if B1 backs up far enough to keep A1 from landing normally, thereby causing contact with A1, it could reasonably be a shooting foul.