Master Overrun (3.5e Feat)
From D&D Wiki
Master Overrun [General]
Your are an expert at the overrun maneuver.
Benefit: You gain a further +2 bonus on Overrun checks. When you overrun an opponent you may make an immediate attack of opportunity against them. This attack is at -4 and causes you to lose your Dex mod to your AC until your next action.
Normal: You cannot attack people you overrun.