Implement knockback

src/main/java/net/minestom/server/entity/Entity.java

@@ -1739,6 +1739,22 @@ public class Entity implements Viewable, Tickable, EventHandler<EntityEvent>, Da
         }
     }
 
+    /**
+     * Applies knockback to the entity
+     *
+     * @param strength the strength of the knockback, 0.4 is the vanilla value for a bare hand hit
+     * @param x knockback on x axle, for default knockback use the following formula <pre>sin(attacker.yaw * (pi/180))</pre>
+     * @param z knockback on z axle, for default knockback use the following formula <pre>-cos(attacker.yaw * (pi/180))</pre>
+     */
+    public void takeKnockback(final float strength, final double x, final double z) {
+        if (strength > 0) {
+            final Vector velocityModifier = new Vector(x, 0d, z).normalize().multiply(strength);
+            this.velocity.setX(velocity.getX() / 2d - velocityModifier.getX());
+            this.velocity.setY(onGround ? Math.min(.4d, velocity.getY() / 2d + strength) : velocity.getY());
+            this.velocity.setZ(velocity.getZ() / 2d - velocityModifier.getZ());
+        }
+    }
+
     public enum Pose {
         STANDING,
         FALL_FLYING,

src/main/java/net/minestom/server/entity/LivingEntity.java

@@ -779,4 +779,18 @@ public class LivingEntity extends Entity implements EquipmentHandler {
         return null;
     }
 
+    /**
+     * Applies knockback
+     * <p>
+     * Note: The strength is reduced based on knockback resistance
+     *
+     * @param strength the strength of the knockback, 0.4 is the vanilla value for a bare hand hit
+     * @param x knockback on x axle, for default knockback use the following formula <pre>sin(attacker.yaw * (pi/180))</pre>
+     * @param z knockback on z axle, for default knockback use the following formula <pre>-cos(attacker.yaw * (pi/180))</pre>
+     */
+    @Override
+    public void takeKnockback(float strength, final double x, final double z) {
+        strength *= 1 - getAttributeValue(Attribute.KNOCKBACK_RESISTANCE);
+        super.takeKnockback(strength, x, z);
+    }
 }