Minecraft wiki entry for Blocking, associated text: Shields are used for blocking incoming attacks. Using one causes the player to slow to a sneaking pace, and after five ticks (0.25 seconds) blockable attacks and knockback coming from the front of the player are negated. Any effects from the attacker (e.g. wither or fire) do not afflict the defender. A successful block is indicated by a sound and the shield taking damage.