Source: Player's Handbook II
By offering Robilar's Gambit, you absorb damage to place yourself in an advantageous position. This dangerous sacrifice is not for the unfit or the unwise, for one failed retaliatory strike can undo the advantage gained. lord Robilar, a rash and impetuous fighter, gained fame using this technique against his enemies.
Prerequisite: Combat Reflexes, base attack bonus +12.
Benefit: At the start of your action, you can adopt a fighting stance that exposes you to harm but allows you to take advantage of your opponents' exposed defenses as they reach in to attack you. Anyone who strikes at you gains a +4 bonus on attack rolls and damage rolls against you. In return, they provoke attacks of opportunity from you each time they swing. Resolve your attack of opportunity after your foe's attack.
Special: A fighter can select Robilar's Gambit as one of his fighter bonus feats.
Normal: Opponents do not provoke attacks of opportunity by attacking. Further, when an opponent provokes an attack of opportunity, you resolve your attack before he completes the action that provoked the attack of opportunity.