Reacting with instinctive speed, you intercept an enemy's attack.

Encounter   ✦     Primal, Weapon
Immediate Interrupt      Ranged weapon

Trigger: An enemy hits an ally adjacent to you with a ranged attack

Target: The triggering enemy

Effect: Make a ranged basic attack against the target with a –2 penalty to the attack roll. Your attack has no effect on the target, whether it hits or misses. However, if it hits, the ally gains a +5 bonus to all defenses against the triggering enemy's attack, and if that attack still hits, the ally takes only half damage from it.

Published in Player's Handbook 3, page(s) 132.