if a shield is implemented, then it need to block attacks, which means setting a threshold of damage, when coming damage lower than the threshold, they are blocked with no harm (can get along with side effect), and only the damage coming from the front.
FYI, the basic wood shield should block 1 damage, then up to Titanium shield, it is so large that can block 30 damage from the front, but it is also heavy that you are slowed by 15%. Or a Tower shield maybe, it blocks 50 damage and incoming projectiles (equivalent to 100 armor... sort of OP), but you can't fly or mount with it, you are slowed to 50%, and you can push enemies back.