(General)
You elbow an ally out of the way, and take his place on the battlefield.
Prerequisites
Base Attack Bonus +1.
Benefit
As part of your movement or as a 5-foot-step, you can move into the space occupied by an ally of your size or smaller, which displaces the ally into the space you just left. Your ally must be willing and able to move and able to occupy the space you were in. This movement does not provoke attacks of opportunity. This does not count toward your ally's movement on his next turn.