You land a heavy blow on your foe, exposing a vulnerable spot in its defenses.

Encounter   ✦     Martial, Weapon
Standard Action      Melee weapon

Target: One creature

Attack: Strength vs. AC

Hit: 2[W] + Strength modifier damage, and the target takes a –2 penalty to AC until the end of your next turn.

Published in Player's Handbook, page(s) 80, Class Compendium.