Backfire

You attempt to interrupt and reverse the effects of a creature casting a spell. If the spell is 3rd level or lower, the creature must make a saving throw with the spellcasting ability used for the spell (Charisma, Wisdom, Intelligence, etc). If the creature fails, the spell backfires, as if the creature had cast it on themselves. The spell stays exactly the same; the creature could potentially make a save against it, or it may not hit its AC, etc. If the creature succeeds on the saving throw, nothing happens and the spell is cast as normal. 

At Higher Levels: If cast at 4th level or higher, it can be used against a spell that is cast at a level equal to the level this spell is cast at. (i.e. if cast at 6th level, it can be used on spells 6th level and below)