Minecraft wiki entry for Combat, associated text: There is a mechanic where when sprint hitting an opponent while holding sprint, the next hit won't be a sprint hit anymore (won't give as much Knockback) and therefore can compromise your combo. It is recommended to reset sprinting after a hit to ensure maximum Knockback to keep a combo, also to keep range (methods such as w-tapping, s-tapping, timed blockhitting, shift-tapping...)