You expend some of your rage to throw one opponent at another.
While raging, when you attempt a bull rush combat maneuver, you can spend 1 additional round of your rage as a swift action to add your Constitution bonus on your combat maneuver check to the bull rush. Further, if you bull rush an opponent into a square another creature occupies or into a solid object, the opponent and the creature or object take bludgeoning damage equal to your Strength modifier + your Constitution modifier.
The text on this page is Open Game Content, and is licensed for public use under the terms of the Open Game License v1.0a.
Sources:
SECTION 15