You interrupt an enemy attack with a clap of thunder, driving the foe back from your friend before the enemy can strike.

Encounter   ✦     Arcane, Implement, Thunder
Immediate Interrupt      Close burst 5

Trigger: A creature hits your ally with a melee attack

Target: The triggering attacker

Attack: Intelligence vs. Fortitude

Hit: 1d6 + Intelligence modifier thunder damage, and you push the target 1 square. If the target can no longer reach your ally, the attack misses.

Published in Forgotten Realms Player's Guide, page(s) 48.