Backlash is a passive warlock ability learned at level 32 for those with the Destruction specialization. It gives the warlock a chance to gain an instant [Incinerate] after being the victim of a physical attack.
This will probably have greatest effect against melee attackers with very fast swing rate such as hunter pets and druids in cat form. Nuke to the face, close range!
Patch 3.1.0 (14-Apr-2009): Has been moved up to tier-5, up from tier-7. Now requires Intensity (pre-req).