Hamstring Attack p. 88
You slice into your opponent's legs, leaving him hobbled and stumbling about.
As part of this maneuver, you make a single melee attack. If this attack hits, it deals damage as normal. In addition, the target takes 1d8 points of Dexterity damage and a -10-foot penalty to speed for 1 minute. A successful Fortitude save (DC 17 + your Str modifier) halves both the Dexterity damage and the speed penalty.