You are trained to take advantage of spellcasters while they are distracted by their own spells.
Benefit: When you attack an enemy who is casting or concentrating on a spell of a level equal to or less than the number of sneak attack dice you possess, you gain a bonus to your attack roll equal to the number of sneak attack dice, to a maximum of +5. (e.g., 3d6 sneak attack grants +3 to attack if the spell is 3rd level or lower, while 7d6 sneak attack grants +5 to attack if the spell is 7th level or lower.) The attack does not need to be a sneak attack for the bonus to apply. You gain the same bonus to Stealth checks made to hide from opponents who are concentrating to maintain spells (regardless of spell level).
Undefeatable: The Collected Feats Sourcebook, Copyright 2009 – 2010, Louis Porter Jr. Design, Inc. Undefeated, Copyright 2011, Louis Porter Jr. Design, Inc.