Crusher feat says:
Once per turn, when you hit a creature with an attack that deals bludgeoning damage, you can move it 5 feet to an unoccupied space, provided the target is no more than one size larger than you.
The once per turn means if you have Polearm master and/or you use your reaction to make an opportunity attack would it activate again since it is not on your turn? And Crusher doesn't refer to "Round" instead?
So, you do your normal turn action and proc the Crusher's feat push. And then when you do an opportunity attack will Crusher push 5ft again?