So I had a situation recently where I’ve had to make a new house rule. My players early into a campaign asked if they could capture a target to interrogate them. I foolishly said I don’t see why your trained adventurers couldn’t do so. Now, they’ve become full kidnap hobos and capture anyone during combat to get answers. Tie onto that…they all have pretty bad persuasion and intimidation rolls. So it inevitably turns into capture the bad guys, ask them questions, fail, ask them the same questions in a different manner. I don’t want to just shutdown the roleplay aspect of capturing people but I do want them to put more thought into it or at least reduce it.

a player may find they have need to capture a target. Maybe they are wanted ALIVE, or perhaps they wish to interrogate them. If they choose to try to capture an enemy, they have 2 physical options aside from story and role playing; they can either KNOCK THEM OUT or DETAIN them. To knock an enemy out, you must audibly say you are trying to do so and then reduce them to 3 HP or less to knock them out, to aid in this endeavor, you may also say you aim to knock them out BEFORE your attack roll and in success, halve the damage of your damage rolls (if a character NAT 20s the attack and it would, even halved kill the target, they are instead reduced down to 1 HP and KNOCKED OUT). To DETAIN an enemy, you must first HAGGARD (a creature is BLOODIED when their HP is half their max HP, furthermore, they are HAGGARD once they are reduced to 10% their max HP) an enemy and then GRAPPLE them. While an enemy is grappled, another creature must assist in DETAINING them by rolling a DC CAPTURE RATE check (D20+ Str or DEX +Prof Bonus; they must also have some way to detain them IE rope, manacles, etc.).

Note: some enemies REFUSE to be taken alive, and will fight past being KNOCKED OUT or will have a difficult DC CAPTURE RATE check to DETAIN (BBEG, Zealots, crazed, enraged, etc)

I’m curious what anyone has to say about this rule, any advice to modify it, or any other tips for capturing enemies. I’d also enjoy reading about some other people’s house rules, how they affect gameplay, and why they were implemented.

That sounds pretty fair to me.  You have made it difficult but not impossible.  You could also make the local authorities frown on kidnapping/torturing/interrogating people  

When I was a kid they had similar rules for subduing a dragon. 

By RAW, you can knock a creature unconscious by declaring you are doing nonlethal damage with a melee attack. Only melee, not ranged, and only attacks, nothing that forces a saving throw. Here’s the bit from the 24 PHB, which is about the same in 14: 

When you would reduce a creature to 0 Hit Points with a melee attack, you can instead reduce the creature to 1 Hit Point and give it the Unconscious condition.

I realize you are saying you are developing a house rule, I just wanted to make sure you understood the RAW. Then, once you knock them out like this, they start a short rest, at the end of that, they regain consciousness. Unless someone heals them, which can wake them up more quickly. 

So, a few things to keep in mind is that mechanics-wise, only melee attacks work, and then the party is sitting around for an hour waiting for them to wake back up. 
Then, again by RAW, that enemy would almost certainly have the hostile condition, so any attempts to influence it would be at disadvantage (which is basically what an interrogation is, influencing them to say things they don’t want to say).

And, you’d be perfectly within your rights as DM to decide an enemy is considered “unwilling” and no amount of rolling will get them to talk. On that, it seems like you might be giving them multiple tries at the intimidation check. Only give one. They can’t just line up and each try a skill check until someone passes. Pass and fail needs to mean something. So, as far as die rolling, it’s pretty easy to shut it down, by RAW, and just say they don’t say anything.

Then, in terms of role play, you can consider who they’re talking to. The bandit captain might know about the bigger plans, but it’s safe to say the lower-ranking guys don’t actually know anything they could talk about, even if they were willing.

Also, just curious, what do they do with people after they interrogate them? If they just kill them anyway, word will get around about these folks leaving no survivors, and people will be even less willing to talk. Conversely, if word gets around they let people go if they talk, enemies might be more open to telling them things.

On Knocking Unconscious

Knocking creatures unconscious RAW is difficult by design. Players have, and should have zero idea how much HP an enemy has. I'm on board with descriptions like the enemy looking as though they can barely hold themselves up to indicate low health; perhaps even being as explicit as 'it looks like one good hit will kill this guy'. In fact, this is what I do in my games. I have a few key phrases that stay in the abstract, but that the players know means 'one hit and this enemy is dead'. At that point my homebrew for knocking a creature unconscious comes into play.

My houserule on knocking someone unconscious is that it can only be done through an unarmed strike. The purpose here was exactly what you describe, to force the players into some thought of how it might be done. That said, in my adventure setting most folks are commoners and have precious few hit points so may not work for your world or setting. I also use the range of enemy HP (i.e. I roll for enemy HP in session prep so players can't metagame how much or how little HP an enemy has even if they are facing six of the same creature).

I would guess though that if you're using Bloodied and Haggard it is because you like the party and players having lots of information to go on. I would just suggest keeping in mind if this information is giving the players licence to play in this style. Without signalling the relative health levels in the way you do, capturing and knocking unconscious becomes a lot more difficult. 

On capturing enemies

First off, you make no mention of enemies fleeing for their lives. For enemies capable of being interrogated, said creatures must also be capable of self-preservation instincts. In which case do you have your enemies try to flee the adventurers at all? For some creatures that threshold might be 50% health, or for others it may be lower. Given the rules for chases, and the complications in the new 2024/5.5e rulebooks that can add in a really fun and interesting dimension to players determined to capture enemies. It also might make it a little more difficult for the party to always be capturing and interrogating enemies. I'd double down on this if the enemy actually does hold useful or pertinent information.

Next up, do you have the captured enemies attempt to escape the binds they are put in. A Slight of Hand Check from the person tying up the captive to set a DC against which the enemy can attempt STR or DEX checks to try and escape creates a potential complication. If that enemy is trying to escape their bonds while the party are attempting to question them it adds a different dynamic. If those enemies are strong enough, or dexterous enough to escape their bonds the party may be forced into a choice to let the enemy escape, or kill them.

'Valuable Information'

The thing that strikes me most about your question here is that the players appear from what you've said to be operating under the assumption that every enemy is going to have some actually useful information. This is the conversation that I'd suggest having explicitly with players. I'd make it clear 'look, not every enemy is going to have useful information'. Think about a real world military or even just basic organisation. Compartmentalisation of information is usually a key strategy. If you've captured a front line soldier, or shop floor assistant they likely have zero information on the larger strategy. For the soldier they might know they've been ordered to go to the local bridge. For the shop floor assistant, they will know that their sales targets have increased. Neither know what is happening at the very top by design. As a result capturing a zombie in Lich's army is going to get a party absolutely nothing useful. Getting hands on a foot soldier in the Dragon's cult might not even tell you where the dragon lives. Anyone with actually helpful or valuable information then is going to be heavily protected, attempt to flee at the first sign of danger, or is going to die before revealing. You might 1 out of 5 times get such an enemy who can be bought, and another 1 in 4 where they will want to save their lives,.

Similarly, how explicit are you being about success or failure of Insight checks? When my player characters want to gauge how honest an answer is they are often put up against a Deception, Persuasion, or Performance check on the part of the person lying or telling the truth. This sets a DC that the player's Insight is aiming to hit. Around six years ago I stopped revealing that DC. I stopped being explicit about if the player character succeeded or failed. Instead, I tend to respond along the lines of 'something in their tone leaves you feeling like they're being evasive' or 'as they speak they never break eye contact, never flinch, either this is a very rehearsed lie or they're telling the truth'. If I want to be explicit, I'll say something like 'you're left in absolutely no doubt that they are telling the truth'.

This style of DMing certainly isn't for everyone, but I do feel is much more immersive. In certain styles of adventure it can also lean into thriller mystery aspects where there's always a little room for doubt. Given that you say you're playing with descriptors like Bloodied, I imagine this kind of style isn't suitable for your table, but on the off chance it's useful I feel like it's worth mentioning. If there's a chance that enemies can successfully lie, or there's no way that player characters can 100% know that the enemy has told the truth, it might just alter their reaction to different situations.


All of this it should be noted however, is meant not to say 'you're playing wrong' but rather to present a different way of things being done from which there might be a 10% chance that something is useful. I am well aware that a lot of GMs disagree with the style I employ.