blood cast: piercing reaction

this spell, Blood Cast: Piercing Reaction, is a reaction only spell. if your Hemocanic Sorcerer is reacting to an attack just made to them, that succeeded, they may use this ability to grapple and disarm the attacking enemy whilst doing double the damage the enemy had just done, back to them, if they fail a DC17 strength save, if succeeded they are only disarmed and take 75% damage