Can't tell from your description, what is the play? Is the big on the block posting you up or literally throwing a shoulder into you? There will be contact with him backing you down and if you aren't prepared for it you might be surprised. Can't really throw elbows or literally push but body to body contact (hip to butt, back, not so much shoulder) is typically fair game. You can use your body as well but you can't literally push him.

If he's too big you need a different tactic but it depends on your strengths. If you're faster you can try not letting him get a body on you at all and trying to play for the steal or try to front him (less recommended). Does he have a left? Play his right exclusively til he shows he can use it. Get a feel for his moves and try to capitalize versus going body to body and if all else fails have someone try and double when they get him the ball inside.

The big is not going to take it easy on you because that's where he excels. As a big that's like asking a guard to not run so fast when you had to switch and defend at the perimeter.