I had a player that did the same.
* First he is not immune to ranged combat, so use ranged combat and molotovs (if they enemies have access to that) can be one way to go. He can still use Small but that is limited to the number of FP he has and using it will also cause a mishap sooner or later.
* In melee, if using scrap spears against him, the enemy can attack from near. If he doesn't have a melee weapon that can attack at near range, he can't use the counterattack stunt.
* In melee, fight the same way he does. Nothing stops you from giving your NPC, the same talents. He wants to be the defensive one to get the most bonus when attacking, but if he thus parries, he can't use the same stunts. Counterattacks will only do weapon damage (and this can't be increased with stunts) and the agility damage stunt can only be chosen once.
* In combat, he wants to parry, do the same. If the enemy has the initiative, do nothing and let him be the attacker. He can of course also do nothing and wait for the enemy to attack. That will be an interesting situation.
* In combat, attack his friends first and when they outnumber him, they use ranged combat first (throwing rocks if they don't have a ranged weapon) or use the defensive approach themselves. Also if he is outnumbered, try to disarm and/or push him to the ground instead of damaging him. Another enemy can take his weapon then.
From a narrative point of view, this wouldn't be so strange to use this kind of tactics against him because a warrior that is so superior in melee fighting will probably be famous because of that.
“I’d say thistles, but nobody listens to me, anyway.” - Eeyore