Brutal Strike( Player's Handbook II, p. 76)
[Fighter Bonus Feat, General]
You can batter foes senseless with your mace, morningstar, quarterstaff, or fl ail. Few victims are willing to stand toeto- toe with a warrior known for knocking his foes witless with a single strike.
Power Attack (PH) , STR 13, base attack bonus +6,
If you use your Power Attack feat to increase your damage with a bludgeoning weapon, you can attempt a brutal strike. You must declare your intention before making your attack. If the attack hits and your opponent takes damage, he must make a Fortitude save (DC 10 + your extra damage from the Power Attack feat on the attack) or be sickened for 1 round. You can use this feat once per round during your attack action.
This feat cannot be used against a creature that is not subject to extra damage from critical hits. A fighter can select Brutal Strike as one of his fighter bonus feats.