My players have been asking to improvise specific combat actions, mostly the archer wanting to aim at specific body parts. I haven't been able to find anything in the DMG or the PHB on the subject so I was wondering how I should deal with this.
How (if at all) should an attack roll be modified when targeting a specific body part? If there is not RAW on this I am open to playtested house rules per Good Subjective, Bad Subjective.
The answers so far tell you how to allow this but don't address the follow-on problem - that the player is looking for a way to disable an opponent without having to eliminate all of their hit points. The problem with allowing this is that you're over-powering the players relative to the NPCs.
So the first conversation should be "if you can do this to opponents they can do the same to you. Are you OK with that?". Then have the party attacked by goblins that use leg attacks to immobilise everyone and kill the party slowly from range. It's going to be unpleasant for the party (so maybe it's better to run that fight as a one-off test with random characters) but it will demonstrate that this is an option that they don't want available to archers. As an aside, I often used mass archers to demonstrate the advantage of tactics and teamwork to arrogant parties - even following the standard rules massed kobold archers can be deadly simply because you can't attack them fast enough.
If you're going to do this it needs to be significantly more difficult (watch someone running - how much does their body move as opposed to their legs?) and higher risk (the chance of someone moving their body aside while the arrow is in-flight is lower than the chance of them moving their arms or legs so the attack has more uncertainty). On that basis it's an option that a high-level archer uses to achieve specific goals (immobilise someone without killing them, for instance) rather than a way for a low-level archer to drop a high-level enemy quickly.
The next problem you need to address is that if you allow the archer to target body parts the next step is two-fold (I've been down this road):
"I shot him in the legs and he's only wearing a chestplate so I should do more damage". By allowing this you're opening the door to the need for hit location armour values. You're going to have to re-define every enemy in the book to handle these house rules and that's time that could be spent writing interesting and challenging scenarios.
"I shoot him in the eye and kill him". Once you allow body part targeting you're a step away from on-demand critical hits.
Remember that there are other games that support this type of combat. DnD doesn't because it's about heroes and adventure and fast, exciting combat. It's not about half an hour of dice rolling for every six seconds of battle. Play the game in the spirit it was built and you'll enjoy it more. I'm worried that this sounds condescending but my experience is that it's easy to get caught up in changing the rules and find that the game becomes more detailed but less enjoyable.
Called shots are a great story device that can make combat seem terrifying and more dangerous, but should never be incorporated mechanically. It creates a situation that slows down combat, which slows down the game and makes it harder for the DM to move the game experience along. It also gives insane and unnecessary power to the players. This isn't to say you can't make the illusion of called shots. I personally like to use damage dealt as my gauge on how I want to describe a called shot.
Example:
Scenario A) You are using a long sword and fighting a rogue with 8 hit points. You deal max damage of 8 on the die. This kills the rogue. You were aiming for his eye? "You drive the point of your blade through his eye socket and out the other end. A small streak of blood races down to the point of your trusted weapon. As you slide your weapon from the rogue's skull, his body goes limp and falls to the cobblestone street." -DM
Scenario B) Same scenario vs the rogue but you deal minimum damage. "You drive the tip of your weapon at his eye, thrusting with precision..." (Because you beat AC, you DID hit.) "... but the rogue sees your attack coming at the last moment and narrowly escapes your fatal strike, leaving but a gash on his brow." -DM
To me, Hit points are a representation of how tough a character is to kill, rather than just how tough they are. The latter of the two is the idea that X weapons sticking out of target = dead target. I call that the pin cushion concept. If you want more realistic combat, you should stay away from this. The first concept is the idea that health points are also a representation of how well a target can defend themselves from blows even after Armor Class has been bypassed. When I do combat with my players, I try to remember that a slashed throat is a slashed throat. There isn't much in the way of coming back from that, so I do my best to rationalize when it is acceptable for a player to be able to cut the throat of a target:
Example:
Let's say you are trying to lop off some brigands head. You are going to deal 10 damage to the target with 10 HP. If he is effectively dead from a single strike, there is little to no reason not to push the idea that your called shot did indeed lop off the head of the brigand especially when, as a player, you don't know how much HP the Brigand had in the first place. For all you know, he had 30 hitpoints and your called shot ended him.
Let's then say the next brigand has 20 hp because he's a higher level than the last. You make the EXACT same strike and deal the same damage. Instead of lopping off his head, he puts up his dagger and it clashes with your blade then he grinds it away from his neck. Unfortunately for him, it still slides into his side and chops through his mid section.
That is the illusion you can create for called shots. No new mechanics. Just good story telling.
As a final note, here are some alternative house rules I've used for called shots and stuff:
I suggest that you do not modify anything, other than describing effects of successful hits according to what the player was attempting to do. E.g. if the player wanted a head shot, and they rolled well and killed an enemy, then it is perfectly fair and in keeping with the game to give them the headshot when you describe the results.
If the archer player really wants a mechanical advantage to represent this effect, then there are two game rules that could help, provided the player is willing to invest in their character's ability to make called shots:
Take a level or two of Rogue to get Sneak Attack for the extra damage.
Take the Sharpshooter feat, where the character can take a -5 penalty to hit for a +10 bonus to damage. It has other benefits for an archer, too.
By RAW, there is nothing in the PHB and DMG that I know of in regard to aiming at a specific part in a fight.
However, in MM p. 291, Troll:
Variant: Loathsome Limbs
[...] Whenever the troll takes at least 15 slashing damage at one time, roll a d20 to determine what else happens to it:
1-10: Nothing else happens
11-14: One leg is severed from the troll if it has any legs left
15-18: One arm is severed from the troll if it has any arms left
19-20: The troll is decapitated, but the troll dies only if it can't regenerate. If it dies, so does the severed head.
[...]
Based on this table, you could apply the same rules to any humanoid, or monster that resembles enough to a humanoid. It is fun for Trolls because then they may regrow 4 arms instead of 2 and even 2 heads, etc. For other monsters, it generally is viewed as gruesome in a game like D&D. But if you do not mind...
Of course, this is not directly aiming at a specific body part since you have to roll a d20, however, it gives an idea of the randomness of attempting to do so.
There is also a note on PHB p. 197:
Describing The Effects of Damage
Dungeons 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.
This generally means that damage, until you reach 0 hit points, do no directly relate to having lost anything. At 0 you may have had an arm or a leg cut off. Until then, your adversary generally tries to hit you hard but with just swords and arrows (except in Hollywood movies) it is rather hard to hit a specific spot in a fight.
You could manage this way, if you don't want to mess with the HP system and still apply called shots.
If you don’t already have disadvantage from any source, you can make a called shot. A called shot is a readied action (the trigger being waiting for an “opening” in the foe’s defense), and thus uses the reaction of the character. The reaction is used after the foe has taken its turn, and the attack is made at disadvantage. Furthermore, certain body parts are considered to have half cover (such as the head and the groin), so it’s even more difficult to hit them.
The attack still does the normal damage, even if you hit the head of a foe: it might only be a dramatic scratch (remember how many fiction characters have scars in their faces, like Rurouni Kenshin). Nevertheless, in a called shot you might want to apply specific effects. The main effect of affecting body parts is applying a condition if the shot is successful. The condition is decided by the player but it must have sense for the attack (such as stunning a foe with the pummel of a sword to the head), and the foe must succeed in a Constitution saving throw to avoid the effect. The DC of the save is the same as the damage done by the attack (EG: if the attack does 8 damage, the save DC is 8).
If the attack is a critical hit, the condition is applied without save. Alternatively, if the attack is a critical hit, you could apply a lingering wound instead of a condition (see the DMG, p. 272).
First, you have a called shot which makes sense in a fight- you have to aim, so you drop initiative until your foe acts. You also don't benefit from multiple attacks, as you can't use the extra attack feature in a reaction.
Second, you can't have disadvantage in the attack to even attempt a called shot, much like the rogue's Sneak Attack, thus you can't "pile" two disadvantages and say "well, I already have disadvantage, so I don't really lose anything if I try".
Third, you still benefit from advantage, but not so much that the Called Shot is an obligated feature, and it is always a tradeoff from a "normal" attack. If you already have advantage, it is cancelled the disadvantage from the called shot, but a normal attack would still have better chances to hit.
Fourth, groin and head are the most protected parts of the body, at least because the arms are moving and covering them so you apply half cover, increasing the difficulty of "one shoting" the head of the foes one more time.
Fifth, you still do normal damage to the character, no matter which body parts you attack. You don't "one-shot" a foe by attacking its head, but you still have a benefit (a condition which must have sense for the attack; no "stun" with an arrow), and the enemy has a fair chance to overcome it (a Con save). In a critical hit, you still have the benefit of auto-succeed the condition or use the lingering wounds rule of the DMG.
I fully agree with @christutty's answer, and I think it should also be pointed out that the existing system already handles striking different body parts: with random damage rolls!
"Armor" and "HP" are not literal absolutes; they're abstract models. Obviously "armor class" doesn't just mean what one is wearing and physically blocking attacks with, but also their ability to dodge hits and simply move out of their way (hence being affected by Dexterity.)
Also remember that although a turn-based system may make it seem like everyone is just standing around and politely allowing each other to make a move while they wait for their turn, in the game's world everyone is actually moving all at once, with "initiative" order representing who is fast enough to act before others.
So when you swing/shoot at someone, the "attack roll" represents your finesse, your ability to lead a target, and it also represents your attempt at aiming for specific body parts.
If you roll high enough for attack, you scored a hit, but the "damage roll" models where you actually struck your target and with how much force.
If you rolled low for damage, then you maybe grazed their thigh or nicked their cheek. If you rolled high, then you struck a vital part with sufficient force.
Critical hits of course represent both a successful aim and also a devastating result.
The target's HP represents their tenacity and ability to continue fighting at full capacity (remember that in a high-fantasy setting like D&D the characters are supposed to be larger-than-life compared to our world, often with the favor of gods.)
Focused attempts such as aiming for eyes or intentionally trying to hobble an opponent are represented by special abilities, such as the Fighter's Disarming Attack, Trip Attack, or the Rogue's Assassinate.
5e was designed to avoid this type of game play.
The critical hit is the closest approximation to hitting a vital organ or just making a great hit.
Adding this level of complexity has the potential to slow the game down, and you'd really need to keep it balanced by making the PCs susceptible to targeted attacks to critical body parts. It would suck for any player to lose an arm during a fight.
Please see this question which although is a different question, it and the answers explain it very well.
Does a gargantuan creature still die if only the feet are ever attacked?
Well there is the Lingering Injuries chart in the DMG, pg. 272, that has sections for losing an eye, foot, leg, arm, hand, getting a limp, breaking ribs, and taking an internal injury, (among others that don't fit this situation). It describes it as
A creature might sustain a lingering injury under the following circumstances... When it takes a critical hit (DMG, 272)
So you could consider not letting them get any special effects to their attack unless they critical, and for bludgeoning damage you could say they break the limb instead of severing it, and if it's bludgeoning to the head, they get stunned for the round.
As for hitting it, you could use the half or three quarters cover rules, depending on the size of the body part. Half for leg or arm (or tendril) or head, three-quarters for a foot, hand, or eyeball. With variation in mind (it's way easier to punch a Beholder's central eye than a human's eye.)
Your player is taking an action covered by the rules, with a complicating factor. Apply Disadvantage to the attack roll.
5e was designed to avoid an ever-compounding fractal of complexity in play. That's why multiple factors were condensed into Advantage / Disadvantage.
Called shots very quickly turn into on-demand critical hits. Some creativity is required to avoid this fate. Be sure to explain to your players that DnD's dice is not a realistic fight simulator, and is never intended to be a realistic fight simulator.
Consider letting your called shots be "fluffy," and hard to turn into measurable tactical advantages. The dice are already balanced to provide the right advantages, so something easily abused automatically is going to imbalance the game. However, there is one final balancing agent in any game: you, the DM. You balance the world the way you like If you want to bring some color into your world, nobody should stop you from doing it.
My recommendation would be to allow for called shots, but explain that their effects will be at your discretion, and generally they will be "fluff pieces." If a normal attack might reduce an enemy to 0HP, a called shot to the eye might be a strike that goes right back to his brain. Tell players they are free to try to turn these fluffy effects into meaningful tactical advantages, but that they should generally expect that they don't do anything numeric. "Called shot: not the face" might be particularly useful when punching a vain opponent who you have to befriend eventually and really don't want to insult. And, of course, as DM you have final say... a called shot doesn't always go according to plan.
Once they're comfortable with this sort of richer combat that doesn't affect the dice, introduce the dice into the game. Offer them a chance to pony up in exchange for effects that are more monetizable. Let them take an attack at a penalty, in exchange for a called shot that might be easier to convert into a tactical advantage. Perhaps the archer says "Called shot: knee, with a -4 penalty," and hits. You might decide that immobilizing the enemy is too powerful in this engagement, so you weave the story that the shot hits, slicing through the muscle of the enemy's lower leg. That, at best, is "fluff." However, that may leave a blood trail to help find the enemy easier, which could dramatically change the way the game proceeds. Maybe a few called shots in a row can start to lead to a more narrative combat instead of less of a dice rolling combat. Find your own balance for how the party is allowed to capitalize on the fluffy results of called shots mid-combat, and don't be afraid to change the mechanics if the party abuses it.
Or perhaps they get a natural 20. In such a case, they did a called shot, give it to them. Let them get the "critical hit" effect of hitting a vulnerable part of the enemy. Let the arrow strike true and tear the knee apart.
The key is that the player gives up something in exchange for an unknown. They have to weigh the clear loss of dice-power against how you, as a DM, choose to handle called shots. They know that each shot is unique. You reserve the right to ruin any called shot you please. Thus, its in their interest to make the called shots interesting. If they can make your world more vibrant, you'll be able to give them more leeway to do what they want.
Potential penalties:
One rule for this sort of play: never give the players the exact rules you use for a particular called shot. You need the freedom to be able to correct for an overpowered kind of called shot. If they know that "Called shot: head" causes dizziness on a roll of 18-20, they'll start abusing it. However, if all they know is "high rolls tend to lead the DM to claim the enemy is dizzy," then you have room to tune the ability. This tuning is both global (affecting every combat), and local (affecting just this fight -- in particular called shots vs. bosses will have to have less capitalizable effects, by necessity).
An example from my table includes an archer sneaking into a gnoll camp.
She failed a Stealth check, but not by much. The result was that a guard spotted her, and she had a brief window to do something before the guard called out and raised the alarm.
Her response was to shoot the guard in the throat to try and silence them.
I had to make something up on the spot, and what I came up with was this: tell me what you want to hamper them from doing (we may need to negotiate it down) and make an attack roll. On hit, you don't deal damage, but they can't do the thing.
Sure enough, she made the shot, and while the idea of a guard taking an arrow to the neck without taking damage from it is a bit ludicrous, it had the desired effect: she got what she wanted in the moment, we established a use case and procedure, and nobody tried to use it for bypassing hit points.
I've been playing D&D for 20+ years, ever since 2nd Edition, and the way a "Called Shot" has always been handled by myself and everyone I've ever played with is that you need to roll a natural 20. It has always been a matter of luck or extreme desperation. Now 5th edition we continue to use this rule in every game I play or DM, but 5e also is a bit different from previous versions of D&D. So, I'd say if your player wants an instant kill it must be a natural 20, but if it's anything else (say shooting a weapon out of someone's hand, getting a bullseye in darts, etc.) just set it as something challenging that takes thier modifiers into consideration and let's the PC show off thier skills and feel cool. Sometimes heroes need to be able to show off.
Somewhere, I remember Called Shots being codified in the rule book. I believe it might have been a DMG thing -- optional rules...
Basically, it was taking a minimum -4 to maximum -10 on the to hit roll depending on the body part targeted. It did not increase the damage done, so no automatic insta-crits or insta-deaths unless narratively useful. Although, it could create narrative points (don't think it listed any explict negative modifiers for if something hit)...like, attempting to shoot at/swing a weapon at the enemy spell casters hand to disrupt the mega-bad ritual they are attempting to cast.
e.g. A leg was -4, while an eye, while wearing a helmet with an eye slit was -10. (I remember it being a table of modifiers.)
Although, I do agree, that trying to do so could only be done so, if you aren't disadvantaged and does not benefit from advantaged.
