Shield Counter

If an enemy misses a melee attack and you are wielding a shield, as a reaction you can
attack with your shield (equal to your proficiency bonus) regain all uses on short rest.

Attack d20+str+pb
Damage 1d4+str Bludgeoning

If you hit the enemy must make a contested con save against your str or be stunned until start of their next turn. If the save succeeds the enemy takes half damage and is not stunned.
If you miss you receive disadvantage against attack rolls targeting you until your next turn.