Would the Disarm optional rule let you use Stunning Strike with it?

Question

Exactly what the title says.

I'm playing a monk in a Tomb of Annihilation campaign. My game plan has been to keep our party alive as much as possible through debuffs, body blocking opponents, and the like.

I recently saw the disarm optional rule and began wondering if you could both disarm and stunning strike as part of the same action. Disarm reads as follows:

A creature can use a weapon attack to knock a weapon or another item from a target's grasp. The attacker makes an attack roll contested by the target's Strength (Athletics) check or Dexterity (Acrobatics) check. If the attacker wins the contest, the attack causes no damage or other ill effect, but the defender drops the item.

Stunning Strike reads as follows:

When you hit another creature with a melee weapon attack, you can spend 1 ki point to attempt a stunning strike

The reasons that I believe this could work is because Disarm specifically calls itself a melee weapon attack, which is all that Stunning Strike requires.
I also says that the foe "Doesn't suffer any other ill effect" so I'm wondering which would take precedence, (e.g. whether or not if Stunning Strike is counted separately from the actual attack.)

Answer 1

No

When you disarm using the optional rule from the DMG, you never hit the opponent with the attack. Stunning Strike requires you to hit an opponent with a weapon attack.

Answer 2

Ask your DM, but it is strongly implied that you could not

Disarm is an optional rule, so you first need to know whether your DM will even allow it. If so, it would also be their call whether you could use a stunning strike on a Disarm attack.

The first step in making an attack is:

1. Choose a target. Pick a target within your attack's range: a creature, an object, or a location.

In looking at the game text, Disarm says (emphases mine):

A creature can use a weapon attack to knock a weapon or another item from a target's grasp. The attacker makes an attack roll contested by the target's Strength (Athletics) check or Dexterity (Acrobatics) check. If the attacker wins the contest, the attack causes no damage or other ill effect, but the defender drops the item.

Although it is not explicitly stated, it is strongly implied here that your actual attack targets the opponent's weapon, not the opponent¹.

Stunning strike, on the other hand, must be accomplished through an attack on the opponent itself (emphasis mine):

When you hit another creature with a melee weapon attack

Although Disarm does not explicitly tell us what the target of its attack roll is, it seems likely that it is the opponent's weapon. Thus you would not be fulfilling the requirement of stunning strike that you hit the creature itself.

However, you are monk and do have a surfeit of attacks compared to other characters. You might even have one or both hands free. Once you have disarmed the opponent, scoop up their weapon with your free hand as a free object interaction and then carry or throw it² far from where they can retrieve it; then make another attack to stun a different opponent. You will need to spend more actions, but at least you will interfere with two opponents rather than one.

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¹_{Anecdotally, of all the weapon-removal techniques I have practiced (usually against knife, occasionally against handgun, staff, or sword) the disarming is seldom accomplished through damaging the opponent, but much more often through manipulating the weapon itself or their grip on it.}

²_{Or, if you are lucky and their disarmed weapon counts as a ranged monk weapon, go ahead and throw it with your own attack.}

Answer 3

No, being stunned is an ill effect (but ask your DM)

Stunning Strike does not allow you to make another attack. Its effect is from the same attack you made to disarm, as you are spending ki when you hit another creature with a melee weapon attack. It's the same attack. When you use it to successfully disarm, the attack causes no other ill effect, because the disarm rule says

If the attacker wins the contest, the attack causes no damage or other ill effect, but the defender drops the item.

Being stunned in combat is an ill¹ effect of the attack. As the attack cannot cause an ill effect, it cannot stun.

Why ask your DM?

Disarm only deals no damage or ill effects if you win the contest. What if you lose the contest? Do you still hit the creature? The disearm optional rule tells you to make an attack roll, and this is what an attack roll means (p. 194, PHB):

To make an attack roll, roll a d20 and add the appropriate modifiers. If the total of the roll plus modifiers equals or exceeds the target’s Armor Class (AC), the attack hits.

Nobody I know normally takes the effort to calculate this under the assumpiton that disarm attacks never deal damage. But on strict reading, you can still hit AC with your attack roll, even if you fail the contest, as long as your roll is high enough to beat AC. And if you have not won the contest, the attack would deal damage or other effects.

This actually makes disarm a lot better, because as written, you would not give up your chance to deal damage for using it, only if you succeed in disarming. We've never played it like that, and felt that disarming is powerful enough to be a fair deal when you have to give up the chance of damage or other effects.

Because Disarm is an optional rule, ask your DM how they play it. They may be OK with this, or they may decide that this is too good, and not not allow disarm at all, or they may decide to tweak the disarm rule, so it either disarms, or fails entirely as an attack.

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¹ Is being stunnded in comabat an ill effect? Ill is not a defined term in the rules. The dictionary, which we refer to for terms not defined by the game, has ill as follows (among others), which fits

• causing suffering or distress
• involving difficulty

Answer 4

If you hit the creature

When you make an attack, your attack roll determines whether the attack hits or misses. … If the total of the roll plus modifiers equals or exceeds the target's Armor Class (AC), the attack hits.

Nothing in the specific rules overrides this general rule.

Your attack roll is compared the AC to determine if you hit, if you do, you can use Stunning Strike.

Your attack roll is compared to the target’s ability check to determine if they are disarmed.

Any given attack could:

1. Hit and disarm - you strike the foe causing them to drop their weapon - you can use stunning strike
2. Hit and not disarm - you struck the creature but they hold onto their weapon - you can use stunning strike
3. Miss and disarm - you strike their weapon causing them to lose it
4. Miss and not disarm - you flail about ineffectually