crazy play

[bpf]

Here is a crazy play for you guys. The way it should be handled will be different on each level so there should be a lot of discussion.

A1 steals the ball from B1 at halfcourt. A1 dribbles towards his basket, picks the ball up, and begins his shooting motion. His teammate A2 is behind him and B1 is behind A2. B1 can't get to A1 so he pushes A2. A2 runs into A1 and knocks him down. The ball pops out of A1's hands and falls to the floor.

What is the call?