Flay( Player's Handbook II, p. 79)
[Fighter Bonus Feat, General]
When fighting unarmored opponents, you excel at twisting your weapon just before impact. This motion rips and tears at your foe's fl esh, causing intense pain. This attack is wholly ineffective against armored foes, but it tears through natural defenses.
Power Attack (PH) , STR 13,
When you use your Power Attack feat with a slashing or piercing weapon against a foe who lacks an armor bonus to AC, you inflict horrid pain on your target. If your attack hits, your opponent must make a Fortitude save (DC 10 + your damage bonus from Power Attack on the strike). If this save fails, he takes a -2 penalty on attacks for 1 round. You can use this feat once per round against a given target.
A fighter can select Flay as one of his fighter bonus feats.