Xeviat
Dungeon Mistress, she/her
But what if the person you're using as a shield has higher AC than you? Then the attack can never hurt them because only attacks that miss you can target them, and those would miss them.The grappled person adds +4 to AC. If an attack misses the grappler by 4 or less, it hits the grappled person.
The random chance to target avoids this issue.