Minecraft wiki entry for Shield, associated text: Shields are used for blocking incoming attacks. Using‌[JE only] or sneaking‌[BE only] causes a player to slow to a sneaking pace, and after 5 game ticks (0.25 seconds)[2], attacks coming from in front of the player are blocked, dealing no damage. When the shield blocks an attack of 3 or stronger, it takes durability damage equal to the strength of the attack rounded up.