weird push play

[rainmaker]

Okay, all you hoop-lawyers, and fellow-arguement-lovers. Here's a weird one for you to "interpret". I actually saw this play. I didn't call it because I wasn't sure WHAT to say!

A1 dribbled into the key, and just as she was going up to shoot, B1 fronted her with good defense and arms straight up. Now as the ball was released, B2 ran up behind B1 and shoved B1's shoulders so that B1 fell into A1 and interfered with the shot. Scramble for the rebound, quick outlet up the floor and I decided to follow the play and worry about that mess later.

So what is it?