AMong "rage powers" is the "Knockback" (even in alpha 3) "Anyone hit by the barbarian’s melee attacks this round is pushed back 5 feet, if possible. This power is used as a swift action before any attacks are made. (4 rage points)".
I feel like it goes against a general rule that no power should affect an opponent regardless of his abilities : then I suggest that the opponent got a saving throw, or that the ability be converted to something similar to an "improved bull rush" feat, or that it gives an additional bonus to bull rush.