Your weapon is busy parrying the enemy's attacks, so you smash your fist into its vitals.

Encounter   ✦     Martial, Weapon
Immediate Reaction      Melee touch

Requirement: You must have a hand free.

Trigger: An enemy misses you with a melee attack

Target: The triggering enemy

Attack: Strength vs. Fortitude (unarmed)

Hit: 1[W] + Strength modifier damage, and the target is immobilized and weakened until the end of its next turn.

Published in Martial Power 2, page(s) 19.