Knock-Down
( Sword and Fist: A Guidebook to Monks and Fighters, p. 7)[General]
Your mighty blows can knock foes off their feet.
Prerequisite
Improved Trip (PH) , Base attack bonus ++2, STR 15+,
Benefit
Whenever you deal 10 or more points of damage to your opponent in melee, you make a trip attack as a free action against the same target.