@JeremyECrawford If you don't have proficiency with shields, do you not get the +2 to AC?
— Jacob Rose (@JRoseYT) November 13, 2019
is WotC staff and somewhat more active on Twitter than JC. Perhaps he’ll drop in with his two copper and that may sate the fighter’s thirst for an official response. The consequences for using armor or a shield with which you lack proficiency are covered on pg. 144 of the Player’s Handbook: disadvantage on attack rolls, ability checks, and saving throws that rely on Strength or Dexterity, and you can’t cast spells. #WotCStaff
— Dan Dillon 👥 (@Dan_Dillon_1) November 13, 2019