How do you handle attacks where the player wants to cut off a target's arm or any specific area? A player in my group today wanted to stomp a creature's back (four footed mammal, dog sized). My solution was to have the player roll for the attack and then roll an ability check to hit the specific place.

On a different topic, how much damage would a kick do and is this an ability check (ex. acrobatics) or a standard attack?

Thank you for comments.

You don’t allow it. Otherwise, everything quickly becomes a head shot. 
Also, rules-wise, hit points are an abstraction that don’t necessarily directly correlate to physical wounds. The game just isn’t set up to handle called shots. And you don’t want to start assigning hit points to every individual body part. It gets unwieldy real quick.

As far as how to handle it. It’s an unarmed strike, roll to hit as normal, damage is 1+str modifier, unless they are a monk, have tavern brawler feat or the unarmed fighting style.

So, I would advise either checking an earlier version of D&D (i.e. not 5e) or a different RPG ruleset for such types of play. 5e isn't great for this kind of style. However, this is how I would run it if my players wanted me to.

Basically, if a player wants to target a specific body part, they must call it before rolling/resolving the attack roll, they can only succeed if they beat the AC by 5 or more. With less than that, but meeting or beating the AC they still hit, but otherwise they don't. This prevents nonsense like 'I aim for the throat' happening every round, but allows the opportunity to still use more targeted and tactical attacks.

The main weakness though is that this has to work both ways - i.e. if the players can target specific body parts, so can enemies with an INT of more than 10. This retains what little balance might exist.

I would then pull the results of the attack off both the damage roll and the Lingering Injuries chart from the Dungeon Master's Workshop in the DMG. So basically, yeah the player can choose to deal specific injuries from that chart, but can't have their unlimited chocie of what they want to achieve. 

My exact words to the last player who wanted to do that was 'if you want that freedom of I can do anything, we'll play FATE instead'. Said player moaned to the ends of the earth, but once introduced to FATE understood what I was getting at. 5e is good at quite a bit, but it's also got downsides.

A player in my group today wanted to stomp a creature's back (four footed mammal, dog sized). My solution was to have the player roll for the attack and then roll an ability check to hit the specific place.

Just have them roll an attack role and damage if the hit.  The attack would be an unarmed strike.  The target takes the damage and no additional conditions unless the character has a feature that applies condition(s) to a target. 

if they crit the attack roll you could let them call the shot insead of dealing double damage, like a less powerful version of a vorpal sword

also you know what would be SICK? vorpal hand wrappings for monks. PUNCH SOMEONE'S HEAD OFF!!!!

"You try to cut off their hand. The enemy, who doesn't want you to do that, moves their hand. You still hit them, but nothing gets lopped off."

Quote from The_Crycket >>

Our group decided we did NOT want called shots after the DM on a one night trial.  Monsters got called shots as well.  One group I was in a called shot was at -5 to attack and a miss was a complete miss not just normal hit.  

 
Yep, players often want advantages - right up until they enemies get those advantages too and then oddly the desire seems to disappear!q

Don’t allow it with few exceptions. The only case I’ve seen ever allowed for this is in CR M9 reunited in the Ukatoa fight.

Tell them to take Sharpshooter or Great Weapon Master the next time they get an ASI.

I rule that they roll with disadvantage, but if they hit a random extra effect occurs. E.g. hits the leg -5ft speed. This can't happen on every shot and maybe introduce a feat like precision shooter that lets them do this.

Quote from Yarrow_Cirdan >>

How do you handle attacks where the player wants to cut off a target's arm or any specific area? A player in my group today wanted to stomp a creature's back (four footed mammal, dog sized). My solution was to have the player roll for the attack and then roll an ability check to hit the specific place.

On a different topic, how much damage would a kick do and is this an ability check (ex. acrobatics) or a standard attack?

Thank you for comments.

 I don't use called shot or Lingering Injuries in my campaigns, usually keeping these guresome outcome for when a foe is killed. 

A kick is an unarmed strike Melee Attacks:

Melee Attacks: Instead of using a weapon to make a melee weapon attack, you can use an unarmed strike: a punch, kick, head-butt, or similar forceful blow (none of which count as weapons). On a hit, an unarmed strike deals bludgeoning damage equal to 1 + your Strength modifier. You are proficient with your unarmed strikes.

I thought the same thing about specific attacks getting out of control. Even though I allowed it, I didn't want to encourage the idea that players could do it at anytime. Thanks.

@martintheactor: Basically, if a player wants to target a specific body part, they must call it before rolling/resolving the attack roll, they can only succeed if they beat the AC by 5 or more. I like this idea. They can try but at a higher cost.

Also, the ideas of hitting only on a critical or using disadvantage are great.

One of the issues I have with allowing it but forcing the character to take disadvantage is that there are way too many other effects that cause you to take disadvantage on an attack.  Since disadvantage doesn't stack, it means that you can fairly safely pack it on if you've already got disadvantage in order to make your attacks more powerful at no extra cost.

As a rule I agree that specific hit locations is a slippery slope. That being said, I do have a 12 sided hit location die that is very useful amusing(sometimes). If a PC has a good reason for wanting to target a specific body part,  I add 25% to the AC, if the attack hits I let them roll the hit location die, they have a 1 in 12 chance of hitting what they want, if they don't roll the specific location they asked for on the hit location D12, then they roll the regular damage, and we move on.

I find the increase to AC (I do not tell them it is a 25% increase, just that it will be higher) alone deters constantly asking. Mostly people stop asking after they have tried it once or twice (except for one Player.... long story). Generally during a fight when the PC knows that the AC for the target is normally 15 and they miss with a 17 because they wanted to hit a specific location, they realize that targeting a specific location is not a good risk vs reward.   

Also, the hit location D12 can make for some very hilarious moments(with proper DM narration)  when the Player says they would like to target the right hand and they hit the left foot instead. I would say that it has been less then 5 times a player has roll the body part they wanted.    

With this I do not allow decapitation, cutting off hands, legs, etc. Mostly people use it to try to disarm. I have always thought that if someone got a Nat 20 on the attack role when they said they wanted to hit a specific location, and they got the location they wanted on the location die, then I would narrate a dismemberment or decapitation..... it has never happened though. 

I don't advertise that  this is an option in my games, I keep the Hit Location Die behind the DM screen until the situation comes up.   My general DM style or philosophy is to try to accommodate players and let them try things. Sometimes  it is better say "yes, but the AC is going to be higher" then just saying "no" and then try to explain why "DnD is not made for this or that" in the middle of a combat round.

This method doesn't really add that much to the rules, and doesn't slow things down that much, and is totally worth it when someone is successful and gets excited!   

Quote from 6thLyranGuard >>

One of the issues I have with allowing it but forcing the character to take disadvantage is that there are way too many other effects that cause you to take disadvantage on an attack.  Since disadvantage doesn't stack, it means that you can fairly safely pack it on if you've already got disadvantage in order to make your attacks more powerful at no extra cost.

 This. And I’d add, coupled with how many ways there are to gain advantage and then cancel out the restriction.

Give this option to a high level fighter with 3 attack per round. One of them is going to going to hit. Then you end up with them 1-shotting what was supposed to be a hard enemy. 

Even by RAW, there’s restrictions on when a vorpal sword works. I’d definitely, at least, look at that for some inspiration, since it’s probably as close as we get to this sort of mechanic of hitting a specific body part in this edition. 

I rule that an attack at a particular body part is at disadvantage. If they hit, no special effects happen. *evil grin*

I have found that if you narrate the hits, players have a lower chance of asking for hit locations.

Player rolls low damage - you just gave him a scratch on his leg, or you nick his cheek, now he's pissed.

Player rolls high damage - you run it all the way through to the hilt, your sword blade is sticking out of its back! or you clobber it in the head, it staggers for a moment because the blow was so hard!

Quote from CharlesThePlant >>

"You try to cut off their hand. The enemy, who doesn't want you to do that, moves their hand. You still hit them, but nothing gets lopped off."

"You try and stab their neck, but they dodge and your spear just scrapes your shoulder."

It's also important to note that an attack that hits and deals damage doesn't actually have to make contact as HP is partially just exhaustion and other stuff (which is wildly confusing to explain lol but it's how it works). And yeah, letting people target specific body parts is hard, though you could represent it by just have higher ACs for certain body parts that hitting deals more damage to.

But honestly, I wouldn't do targeting anything vaguely like that unless it's like a 1v1 duel and you wanna add a buff without consequences by letting a player hit certain body parts and do cooler stuff and be more cinematic on higher rolls.