You strike at the exact right moment to interrupt your opponent’s spell, causing it to backfire and disrupt nearby spellcasting.
Benefit: When you successfully interrupt an opponent’s spell with a physical attack (not a spell or continuous damage), the spell backfires, causing a small burst of energy which affects all creatures within five feet of the caster (including the caster). Any creature caught within the burst who is concentrating on a spell must make a concentration check (DC 10 + the spell’s level + the number of sneak attack dice you possess) to maintain the spell. In addition, any creature caught within the burst who attempts to cast a spell within the next round must make a concentration check (same DC as above) or lose the spell.
Undefeatable: The Collected Feats Sourcebook, Copyright 2009 – 2010, Louis Porter Jr. Design, Inc. Undefeated, Copyright 2011, Louis Porter Jr. Design, Inc.