Pack Tactics

 
Prerequisite(s): Wis 13+.
 
Benefit: Whenever you flank an opponent, an ally not flanking that foe gains a +1 bonus on melee attacks made against your flanked opponent. Flanking allies retain the normal +2 bonus on melee attacks.
 
Special: A fighter may select Pack Tactics as one of his fighter bonus feats.
 
Source: Dragon Compendium