Over the Back

While watching an NCAA game the other night A1 is fouled during a rebound attempt by B1 who comes over his back from behind.
L calls the foul and while reporting to the table he makes a motion with his arm coming down in front of him in a high arc indicating what the call obviously was for.
Unfortunately, you never get to see the officials on TV actually reporting the foul. My question is, since we all know there is no actual 'Over the back' foul signal, how would that be properly reported to the table. Illegal use of hands?
What if the contact was made by B1's torso on A1's back? Would it constitute a charge or push from behind?
I've seen coaches yell at refs for "over the back!" just for players reaching over for the ball with no contact. No contact, no foul correct?