Minecraft wiki entry for Sword, associated text: After the Combat Update, the sword blocking functionality was replaced by blocking with shields and to accommodate the dual wield system. Shields negates more damage and knockback than sword blocking from "blockable" attacks (they block 100% damage and knockback after Java Edition 1.11), but, unlike swords, they have a 0.25 second startup period before damage can be mitigated and can be temporarily disabled by attacks with an axe.