Chief and Locke’s fight, while awesome, had some major flaws in it.
Firstly, damage sustained by both fighters (Chronological).
Chief took: several knees to the stomach, kick to the top of his helmet, single punch to helmet, uppercut to the visor, his own headbutt.
Locke took: Battle Rifle being broken across his face, judo flip, two punches to the face, knee to unarmored abdomen, headbutt.
Chief took substantially less damage than Locke, but walked away in worse shape.
At the very start of the fight, Chief rips Locke’s BR out of his hands, and proceeds to, for lack of a better term, slap him with it. If you look closely, you can see fragments of the weapon’s stock fly through the air between them. This means that Chief is swinging this thing with the intent to knock Lock unconscious. A normal BR can survive multiple fatal hits from a Spartan’s melee attacks, but Locke remained entirely conscious and combat capable. Given the strength capacity of Chief, and the speed the stock was traveling upon impact, he could have been hit with a force somewhere around having a car hit your head going 30+ miles per hour. Logically, he has a concussion, potentially internal bleeding, and maybe even some issues with his neck. That should have been the end of the fight.
However, they go into a bit of a wrestling match over the Armor Restraint, during which, Chief lands a solid punch to Locke’s helmet, followed by another backhanded strike as he brought his hand back to its proper side. He also landed a knee to the unarmored side region of Locke’s midsection. This is hit that would damage the soft tissues on his right side, or at the very least, have him feel some pain and recoil from it.
Chief’s helmet has two portions above his eyes that protrude outwards. While these are not jagged, they can concentrate force in a much greater way than a standard human skull. This means that his headbutt would have dealt a fair deal of damage to Locke’s helmet.