Do I get the +2AC from a shield if it stays on my back all the time? Another way to look at it: If I use my Versatile weapon as two-handed, does my AC go down? I'm still proficient in all my gear, so I know I keep my proficiency bonus.
The PHB says (p. 144) "A shield is made from wood or metal and is carried in one hand. Wielding a shield increases your AC by 2."
My instinct says I lose the +2, but thinking realism/role playing, maybe only on attacks from behind?