I was watching the Nova special on the Kennedy assassination and I saw something remarkable. They fired a rifle bullet through three feet of pine wood boards and the bullet looked nearly pristine. Then they fired the same type of bullet into a human skull filled with ballistic jelly. Half of that bullet had disintegrated.
Think about that for a moment. In terms of damage to the weapon, an inch or so of human skull is harder than three feet of wood. Imagine how hard you have to be striking to actually crack the skull. And how damage that is causing to your weapon in the process.
Of course cracking the skull isn’t required. The combination of a bleeding head wound and a concussion can certainly end a fight. Though it make take a few seconds (minutes?) for the effects to be felt and you’ll have to defend yourself in the mean time.