A1 gets fouled by B1 in the act of shooting. Whistle. After missing the shot, A1 thinks swings his fist is personal disappointment. Fist hits B2, who happened to be walking by, in the face.

Everyone in the gym KNOWS it wasn't intentional. Got a call?

Yes. There are still ramifications for A1's actions. Flagrant T and he's gone. It makes no difference whether it was intentional or not.

4-19-4
A flagrant foul may be a personal or technical foul of a violent or savage nature, or a technical noncontact foul which displays unacceptable conduct. It may or may not be intentional.

I once had a kid who had rebounded the ball and had defenders all over him. I called the foul. I take two steps and the kid inadvertantly threw an elbow that nailed an opponent in the face. He went to the floor scremaing, blood everywhere. T and gone.