What ability check is the most appropriate for disarming a weapon from a creature grappled by another party member?

Question

It's my first post here. I am a DM running a 5e campaign for my friends.

During our last session, the characters were surprised by a creature polymorphed to look like a friendly NPC. The creature took their friend's weapon (a one handed mace) and was using it to attack them. One of the party members had jumped off a cart and put themselves and the creature into grappled and prone condition states on the ground.

A different party member approached and said "I want to grab the weapon from [the enemy] and toss it away." In response, I asked for a Dexterity (Sleight of Hand) check to see if they could remove the weapon. Was this the best-fit ability check for this scenario?

My reasoning for the check was:

1. The Grappled nor Prone conditions state anything about the enemy being disarmed or losing control of their weapon (Players Handbook, Grappled - pg. 290, Prone - pg. 292), so I saw the active fighting and resistance displayed by the antagonist as creating a situation where it wasn't an easy feat to simply grab the weapon.
2. I think the action would require precise, dexterous movement of the hand to grab it while the enemy flails and combats their assailant. PHB states Dexterity ability checks "measure agility" (PHB, pg. 173).
3. Sleight of Hand use on pg. 177 of the PHB doesn't state anything about removing a weapon, just subtly removing a coinpurse without the person knowing. However, I also interpret it as the ability to manipulate an object on another's body in a tricky situation.

After thinking on it, I feel as though a Strength (Sleight of Hand) check may have been more appropriate because the PC wresting the weapon away was a dwarf not prone to stealthy actions, but I would love some feedback on more specific rulings I'm missing.

Thank you for any help you may provide.

Answer 1

The DMG suggests an attack roll for Disarming

There's no standard option for disarming opponents, however there is an optional rule in the Dungeon Master's Guide (page 271). It has the attacker (disarmer) make an attack roll contested by Strength (Athletics) or Dexterity (Acrobatics). It also gives some clauses for advantage/disadvantage neither of which relate to grappling (you may of course grant either regardless of that). The prone condition influences the attack roll as normal.

Answer 2

There are some available rule options

As SomeoneEvil answered, the DMG provides an optional rule for allowing a specific disarming attack.

This suggests that this attack is purely an optional rule that a DM can choose to employ, but that's not entirely correct.

The PHB covers this as well with the Disarming Maneuver by the Battlemaster Fighter.

When you hit a creature with a weapon attack, you can expend one superiority die to attempt to disarm the target, forcing it to drop one item of your choice that it’s holding. You add the superiority die to the attack’s damage roll, and the target must make a Strength saving throw. On a failed save, it drops the object you choose. The object lands at its feet.

So how should you approach this?

This is entirely up to you, and as others have said, you did a great initial job. Your players came up with an idea and you gave a ruling and are now verifying your ruling after the game.

In vanilla play, the Fighter is the only one who gets an option to disarm. There is a little (but not much) concern in allowing the optional rule in the DMG to provide another tactic to all classes - and their ability to do it is limited by their Superiority Dice. Making this option always available does step a little bit on the toes of this class build.

But what you really should remember that if this becomes a common tactic in your world/with your players, that enemies can and should do the same to the players. If it's good and usable for them, it is for NPCs as well.

I'd recommend talking with your players and seeing what they, and you, are comfortable with.