Is it legal to push back the opponent while posting

[Adam]

Originally Posted by Camron Rust

So, if A2 wasn't displaced, that means that A2 is applying just as much pressure in the opposite direction....Newton says so.

So, who is really doing the pushing? One player wants to move their opponent in, and the other wants to move their opponent out.....or they want to resist being displaced. Both are applying pressure in roughly equal amounts. Only when one displaces the other (or it becomes too rough) does the contact become a foul....and either one could be the guilty party.

Not necessarily, inertia plays a factor, as does size difference.