Forceful Impacts (3.5e Feat)
From D&D Wiki
Forceful Impacts [General, Fighter]
Your blows with melee weapons can push enemies on successful strength checks.
Prerequisite: Power Attack, Str 16, Proficiency with all martial weapons or any exotic weapon
Benefit: Once per round and only against one enemy, when you strike an enemy with a martial or exotic weapon, you may make a strength check opposed by your opponent to push them 5ft along the direction of the strike. You may not gain this benefit when fighting defensively. If the push would put them in an occupied space or in a space they cannot be pushed into, they are instead slowed for one round.
Normal: You cannot push opponents on successful weapon attacks.
Special: Enemies can be knocked airborne(as with an upward slash), to the left or right(as with a swipe to the side), or backwards(as with a stab), but cannot be pulled towards you or forced into the ground. This forced movement does not provoke attacks of opportunity.