You thwart an enemy's attack with a timely thrust of your blade or a quick shot from your bow.

Encounter   ✦     Martial, Weapon
Immediate Interrupt      Melee or Ranged weapon

Trigger: You or an ally is attacked by a creature

Target: The attacking creature

Attack: Strength vs. AC (melee) or Dexterity vs. AC (ranged)

Hit: 1[W] + Strength modifier damage (melee) or 1[W] + Dexterity modifier damage (ranged). The target takes a penalty to its attack roll for the triggering attack equal to 3 + your Wisdom modifier.

Published in Player's Handbook, page(s) 106.