Overhead Thrust( Draconomicon, p. 106)
You can deal a nasty attack to anything that tries to crush or run over you.
You can use a slashing or piercing weapon to make an attack of opportunity against a foe using an attack designed to batter you from above, such as an overrun, trample, power dive, or dragon crush attack. You cannot use this feat if you are flat-footed or already grappled. This feat does not grant you an additional attack of opportunity in a round, so the feat does not help you if you have no attacks of opportunity available. You gain a special attack modifier based on your opponent's size, as shown below. If your attack hits, you deal triple damage.
|Medium or smaller||+0|
Any extra damage dice your attack deals (such as from a sneak attack ability or a weapon special ability) are not multiplied by this feat. If you score a critical hit with your attack, the extra damage you deal stacks with the extra damage from this feat. Add the damage multipliers together according to the standard rule (see Multiplying, page 304 of the Player's Handbook). For example, if your weapon deals double damage on a critical hit, any critical hit you score while also using this feat deals quadruple damage.