Pushing foul or traveling violation.

[egausch]

Most refs will wait for one good tug before calling a held ball, when both A1 and B1 have their hands on it. What if B1 purposely lets go or even pushes rather than pulls in an attempt to have A1 pull and fall backwards? I can't see a personel foul here, but maybe unsportmanlike or a travel on A1. Off the top, I would tend toward the unsportsmanlike because B1 is not directly playing for possesion of the ball.
EG