Using a sword to block (right-click) while attacking (left-click) reduces incoming knockback by approximately 50% in 1.8.9.
: Advanced clients allow users to set specific percentages (e.g., 50% KB) to make the cheat harder to detect for anti-cheat systems Movement Locking anti kb mod 1.8.9
In 1.8.9, knockback is calculated server-side using: Using a sword to block (right-click) while attacking