Blade Ward

Abjuration Cantrip (Bard, Sorcerer, Warlock, Wizard)

Casting Time: Action
Range: Self
Components: V, S
Duration: Concentration, up to 1 minute

Whenever a creature makes an attack roll against you before the spell ends, the attacker subtracts 1d4 from the attack roll.

Source: Player's Handbook, p. 247