Shield Strike

The best defense is a good offense. While wielding a shield, you can utilize it offensively, and replace your attack when you take the Attack action with a Shield Strike; Str is the Attribute used, and you add your proficiency bonus to the attack roll. A successful Shield Strike does 2d4+Str Bludgeoning Damage, and the creature you hit has disadvantage on it's next attack roll before the start of your next turn. If you have Extra Attacks, you can replace any Attack you make during the Attack Action with a Shield Strike.

A magic shield adds any additional bonus it has to the attack and damage rolls of this skill, and allows it to bypass magic resistances. 

Additionally, as a Bonus Action, you can enter a stance that lasts until the start of your next turn, granting yourself or an ally within 5' half cover with your shield.