Polo Rules

But a shoulder can be used to "make space", with the forearm rule, at least how it seems to be meant to be called, it shouldn't be.

So if you are on the ball, and someone is on your steering side, they can't really hit you hard with it.

If you are the defender, and the player on the ball is next to your stearing arm, it's really up to you how hard you go in against their forearm.

So to me it would seem safer (if infractions are called).

Disagree. I can do a lot more damage to someone with a forearm than I can with a shoulder.