You attempt to interrupt a creature in the process of casting a spell. If the creature is casting a spell of 5th level or lower, its spell fails and has no effect, and the caster takes 1d10 force damage per level of the spell. If it is casting a spell of 6th level or higher, make an ability check using your spellcasting ability. You can add half your proficiency bonus (rounded down) to this ability check. The DC equals 10 + the spell's level. On a success, the creature's spell fails and has no effect. If you succeed on the ability check by 5 or more, you turn back some of the spell's magic toward the caster. The caster takes 1d10 force damage per level of the spell. If you fail, the spell is successfully cast, but any creatures who must make a saving throw have advantage. If you fail by 5 or more, the spell is successfully cast.

At Higher Levels. When you cast this spell using a spell slot of 6th level or higher, the interrupted spell has no effect if its level is less than or equal to the level of the spell slot you used. In addition, the caster takes 1d10 force damage per level of the spell.