Overwhelming Assault

 
Prerequisite(s): Base Attack Bonus 15+.
 
Benefit: As a free action, designate one specific foe as the target of this feat. If this foe begins his turn adjacent to you, ends his turn still adjacent to you, and does not attack you, target you with a spell, or use a special ability against you, you gain a +4 bonus on melee attack rolls against him on your next turn.
 
Source: PHB II