Thornskin

You touch a willing creature and their skin transforms to resemble a bramble of thorns. Until the spell ends, whenever they are hit by a melee weapon or spell attack from a creature within 5-feet of them, the attacking creature takes 1d4 piercing damage.

At Higher Levels. When you cast this spell using a spell slot of 4th level or higher, the damage increases by 1d4 for every two slot levels above 2nd.