Your Ambush and Backstab hits have a X% chance to unbalance a target, increasing the time between their melee and ranged attacks by 20%, and reducing movement speed by 50% for 8 sec.
Patch 3.3.3 (2010-03-23): The debuff from this talent can now be caused by Backstab in addition to Ambush and can be triggered by all hits from these abilities rather than just critical strikes, but the snare component is now 50%, down from 70%.