maybe resistance to non-lethal damage is appropriate?
I think you are confusing 5e rules with previous editions.
There is no such thing as non-lethal damage in 5e.
[sblock=Damage Types from the 5e Rules]Different attacks, damaging spells, and other harmful effects deal different types of damage. Damage types have no rules of their own, but other rules, such as damage resistance, rely on the types. The damage types follow, with examples to help a DM assign a damage type to a new effect.
Acid. The corrosive spray of a black dragon’s breath and the dissolving enzymes secreted by a black pudding deal acid damage.
Bludgeoning. Blunt force attacks—hammers, falling, constriction, and the like—deal bludgeoning damage.
Cold. The infernal chill radiating from an ice devil’s spear and the frigid blast of a white dragon’s breath deal cold damage.
Fire. Red dragons breathe fire, and many spells conjure flames to deal fire damage.
Force. Force is pure magical energy focused into a damaging form. Most effects that deal force damage are spells, including magic missile and spiritual weapon.
Lightning. A lightning bolt spell and a blue dragon’s breath deal lightning damage.
Necrotic. Necrotic damage, dealt by certain undead and some spells, withers matter and even the soul.
Piercing. Puncturing and impaling attacks, including spears and monsters’ bites, deal piercing damage.
Poison. Venomous stings and the toxic gas of a green dragon’s breath deal poison damage.
Psychic. Mental abilities such as a mind flayer’s psionic blast deal psychic damage.
Radiant. Radiant damage, dealt by a cleric’s flame strike spell or an angel’s smiting weapon, sears the flesh like fire and overloads the spirit with power.
Slashing. Swords, axes, and monsters’ claws deal slashing damage.
Thunder. A concussive burst of sound, such as the effect of the thunderwave spell, deals thunder damage.[/sblock]
I think the game designers took out non-lethal because they are making damage more abstract to match HP and damage is lethal until the foe is reduced to 0HP. Just because you reduce someone’s HP, doesn’t actually mean they took any real damage. For example, the fireball’s flames singed the target’s hair and some exposed skin, scaring the crap out of him (translation: took 25 of 30 HP).
In previous editions, common thinking is that Damage = Wounding. But HP were never about how many wounds you could take then either. Spells like Cure Serious Wounds further supported that way of thinking.
I like that 5e really clarified this concept compared to other editions, yet they did not actually change anything much. I never really liked the idea of NL damage when Lethal Damage had no real affect either. Trying to write combat results at higher levels was making no real sense until I adopted the same thinking as they describe for 5e.
Look at these excerpts from the 5e rules:
Describing the Effects of Damage
Dungeon Masters describe hit point loss in different ways. When your current hit point total is half or more of your hit point maximum, you typically show no signs of injury. When you drop below half your hit point maximum, you show signs of wear, such as cuts and bruises. An attack that reduces you to 0 hit points strikes you directly, leaving a bleeding injury or other trauma, or it simply knocks you unconscious.
Dropping to 0 Hit Points
When you drop to 0 hit points, you either die outright or fall unconscious, as explained in the following sections.
Instant Death
Massive damage can kill you instantly. When damage reduces you to 0 hit points and there is damage remaining, you die if the remaining damage equals or exceeds your hit point maximum. For example, a cleric with a maximum of 12 hit points currently has 6 hit points. If she takes 18 damage from an attack, she is reduced to 0 hit points, but 12 damage remains. Because the remaining damage equals her hit point maximum, the cleric dies.
Falling Unconscious
If damage reduces you to 0 hit points and fails to kill you, you fall unconscious. This unconsciousness ends if you regain any hit points.
When you look at this, what is the mechanical difference really between unconscious due to injury versus just being knocked out? None, so why would you need a roll to check if you succeed instead of letting the player decide?
This leads me to another issue…
Referencing reality to nit-pick at rules is backwards for me. That is because we are playing a role-playing game, not a mechanics heavy roll-playing game. All the rules for combat are doing is structuring things to allow the participants to tell the story with some randomness applied to the outcomes. We could simplify things to coin flips and still accomplish the same thing from a role-playing perspective. Flip a coin to see if you hit. Flip again to see if you killed. Then write your results as creatively as you want that makes realistic sense.
Instead of trying to make the game mechanics fit reality, I just use them to help realistically write the results of actions in the story. The game mechanics purpose is to allow adjudication for the actions I want my character to do. If I want my highly trained fighter to simply knock out his opponent with the hilt of his sword instead of breaking his skull, then it should happen.
