Polo Rules

As long as your arm is bent less than 90 degrees, you can make contact as you wish.

You are allowed to push, as long as the elbow isn't extended more than 90 degrees.
Is it more than, or less than? And which side of the angle are we measuring this from?

My understanding is that the angle formed inside the elbow should not be more than 90 degrees, i.e. if you fully extend your arm, the angle is ~180 degrees.
As the arm flexes, and the wrist moves up toward the shoulder, this angle decreases.