Force Reactive Disk

Force Reactive Disk is an Engineering-made shield that shocks nearby enemies when the shield blocks. It does about 30-40 points of damage to enemies within 10 yards. Unfortunately the shock can also break crowd control such as polymorph, sap, hibernate, etc. For every block, there's a 50% chance the shield will lose 1 point of durability.

Source
This item is crafted with Engineering (300); taught by Schematic: Force Reactive Disk, a drop from bosses in the Molten Core.

Background
A gnome tinker living in Ironforge originally developed this device, which has since been expanded into a full size, round tower shield for military use. The force reactive disk looks to be an ordinary (if circular) tower shield, except for a series of metal studs arranged across its surface. Dwarven craftsmen of exceptional skill often arrange these studs in decorative patterns without affecting the device's function. Twisting a control dial inside of the shield activates a shimmering screen of electricity coursing among the external studs.