Weapon utility when used in confined spaces?

Question

So the characters are invading a small goblin lair. Rather than having the lair's tunnels be 10×10 feet and the rooms large and man-sized, the tunnels are 4 feet tall and 2½ feet wide and the rooms are the size of small cars.

How would you adjust weapon efficacy—both to hit and damage—when fighters can't swing their swords and axes, etc? I can't see a fighter wielding his greatsword or greataxe with any real efficacy with so little room. Especially in the tunnels where their shields can barely fit.

Piercing weapons like daggers and short swords would work but a long sword? A greatsword? Even if the PC suffered a disadvantage it's difficult to see a greatsword inflicting normal damage under such circumstances.

Axes and hammers would be useless, I expect: Can you picture someone wielding a maul in such limited space?

How do you adjust advantage/disadvantage and damage in such confines? Should some weapons be considered useless? Wouldn't two weapon fighting and two handed weapons be affected more than small and piercing weapons?

Answer 1

“Underwater Combat” rules provide a framework for unfriendly environments

There are basic rules on PH p.192, under Squeezing Into a Smaller Space for dealing with creatures in spaces too small to accommodate them. These don’t go into the level of detail you are suggesting, involving restrictions on various weapons.

It sounds like you wish to create a feeling of the characters being “out of their element” in the cramped goblin warrens. The game designers accomplished this with their Underwater Combat rules. These rules can serve as a framework for any unfriendly environment.

Here is what you would do for melee weapons:

1. Identify melee weapons that will work normally, and those that will have disadvantage.
2. Identify creatures that are “in their element” and can ignore Rule 1.

For your goblins, the ability to use any weapon may be irrelevant, if they are using “standard issue” short swords and short bows. But you may wish to rule, for example, that any small or smaller creature has room to use any of their weapons effectively.

This is the quick and fun way to handle such environments. The party may want to adjust their tactics a bit, but (used in moderation) no player should feel frustrated about their character being made ineffective.

Useless weapons are like monster immunities

If you go beyond sorts of things in the “Underwater Combat” rules, then you may have some work to do for play balance. If you make certain weapon completely unusable in the caverns, you effectively give the denizens immunity to damage from those weapons.

The Creating a Monster: Step 9 section of the DMG (p. 277) states:

Giving a monster resistances and immunities to three or more damage types (especially bludgeoning, piercing, and slashing damage) is like giving it extra hit points.

In your case, monsters would only be immune/resistant to some weapons, but you are probably still limiting some of your PC’s damage expressions. Take your specific case into consideration (that is, how the damage expressions of the PC’s in your party would be effected) and determine if you should apply the challenge rating modifiers in the Effective Hit Points Based on Resistances and Immunities table on DMG p. 277.

Don’t spring the rules on your party

Especially if you go beyond the “Underwater Combat” style rules, make sure you give your players fair warning about whatever strictures you would impose. If a passageway is too cramped to use a PC’s favored weapon effectively, the character should realize that.

Be aware, if you make the environment too unfriendly to the party, they may simply decide not to enter.

Answer 2

There are Options, but You Could be Inviting Trouble

All of your points are interesting, and accurate. Several weapons, like warhammers or flails, do rely on wide swing to generate power, while others like pikes and daggers rely on forward thrusting, which would be less limited in these settings. It would make some sense that certain weapons would be more effective than others in such an environment.

There is advice in the PHB for using a weapon in an unusual way. On page 147-148 of the PHB, it mentions rules for Improvised Weapons, which are usually items which are not intended to be used as weapons, and deal 1d4 damage. But it also mentions:

If a character uses a ranged weapon to make a melee attack, or throws a melee weapon that does not have the thrown property, it also deals 1d4 damage. -PHB p. 148

This gives some precedent for the idea that using a weapon in a manner it is not intended to be used (jabbing with a warhammer, for example) can count as an "improvised weapon".

However, keep several factors in mind:

1. There are established rules for fighting while in a space that is too small.

While squeezing through a space, a creature must spend 1 extra foot for every foot it moves there, and it has disadvantage on attack rolls and Dexterity saving throws. Attack rolls against the creature have advantage while it’s in the smaller space. - PHB p. 192

2. This decision likely doesn't just apply to this one combat. Players will expect that rules which apply to them apply to others as well. In future encounters, players might ask you many questions about whether a dragon's claw attacks count as "improvised" in a vine filled jungle which gets in the way of its swings, or if a giant's attacks count as "improvised" since their weapons are designed to fight other Giant sized creatures.

3. Weapons are versatile. A slashing weapon can stab, a piercing weapon can bludgeon. It is worth noting environments (like being underwater) which would particularly inconvenience particular varieties of weapons. But penalizing some weapons more than others may feel unfair to some players.

Bottom line: You might be making a lot of work for yourself.

Although the rules for fighting in a small space are overly simplistic, they do save a lot of time that otherwise might go into considering the details of the length and use of weapons. For example, a Pike is Heavy, Two handed, and has Reach: but it relies on thrusting and thus would work well in a tunnel. On the other hand, a War Pick is one handed, does piercing damage, and is not Heavy: but it relies on swinging and thus might not work well in confined spaces. It would take a lot of thought to figure out exactly what weapons would or wouldn't fall under the "improvised category". And unless you're willing to do such complicated thinking not only now, but in every atypical environment, I would advise against too much tinkering.