What is a damage roll?

Question

How do the rules define Damage Roll?

Example, a Hexblade Rogue hits and rolls damage for attack with

• a short sword (1d6 piercing),
• as a sneak attack (2d6 piercing),
• while Hex spell is active on target (1d6 necrotic),
• with blade coated with Serpent Venom (3d6 poison, save for half),
• adding Valor Bard's Combat Inspiration (1d6, piercing?)

How is this attack divided into separate Damage Rolls? Or is this all combined together to just one instance of rolling the damage dice?

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Another example, where this might be relevant. This is a bit contrived example, but certainly possible even for PCs for example with effects that drain strength, or if stats are rolled:

A creature with Strength modifier -3 attacks with a +1 magic club with aid of Valor Bard's Combat Inspiration 1d6, and rolls 1 with 1d4. Combat inspiration damage is 3. Minimum damage is 0, so this can either be

max(0, 1 from dice 
       +1 from magic weapon 
       -3 from strength) 
+3 from combat inspiration 
= 3

or

max(0, 1 from dice 
       +1 from magic weapon 
       -3 from strength 
       +3 from combat inspiration)
= 2

Depending on just where the "minimum damage is 0" rule is applied.

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For reference, the Basic rules say this about Damage Rolls but it doesn't really answer above:

Damage Rolls

Each weapon, spell, and harmful monster ability specifies the damage it deals. You roll the damage die or dice, add any modifiers, and apply the damage to your target. Magic weapons, special abilities, and other factors can grant a bonus to damage.

With a penalty, it is possible to deal 0 damage, but never negative damage.

When attacking with a weapon, you add your ability modifier--the same modifier used for the attack roll--to the damage. A spell tells you which dice to roll for damage and whether to add any modifiers.

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^{(This question is inspired by this more specific question about Grave Domain Cleric's Grave Touched feature.)}

Answer 1

"Damage Roll" doesn't have a hidden meaning

It just means any roll of damage dice. The rules don't actually say about "damage rolls", the terms "damage" and "damage dice" are used instead:

• "damage" — a numeric quantity with a specific damage type
• "damage dice" — any dice which are used for calculating damage

These terms are described in the "Damage Rolls" chapter, but "Damage Rolls" is just a name of the chapter, not a specific kind of rolls:

You roll the damage die or dice, add any modifiers, and apply the damage to your target.

See also Does "flat" damage count as a "damage roll"?

The PHB indeed has a few mentions of "damage rolls" or "weapon damage rolls", but they mean nothing special but rolling some damage dice. Compare this to an explicitly defined kinds of rolls:

Ability checks, attack rolls, and saving throws are the three main kinds of d20 rolls

Both damage and damage dice can be modified in some cases. "Damage dice" are doubled when there is a crit. "Damage" can be doubled or halved depending on resistance/vulnerability. Since addition is commutative, you can roll damage dice in any order, either sequential or simultaneously — the result will be the same.

The only case when it does matter is the Instant Death (a.k.a. "massive damage") rule. But this doesn't depend on what a "damage roll" is, it just depends on damage itself. See Is damage from multiple damage types cumulative for death and massive damage?

Critical Hits description is a bit inconsistent

The generic rule is:

Roll all of the attack's damage dice twice and add them together.

One can think only weapon damage dice should be doubled. However, spell attacks can score a critical hit. Features like Sneak Attack can deal double damage as well. The PHB says about this explicitly in relevant chapters. See See How does extra damage work for critical hits?

Answer 2

It's all the damage dice that come specifically from hitting with the attack.

There isn't a clear and easy standard for this that applies across the board, but in general "the damage roll" is all the dice that apply to the attack, once you've factored in sneak attacks, smites, certain spells, or any other effects that the player gets to add in.

However, the damage roll should not include any damage that's behind a saving throw triggered by the hit, such as poison. If the attack makes the target roll a save, any damage subsequent to that is related to the result of that saving throw, not to the attack. Those should not be considered part of the attack at all -- they wouldn't be double-rolled on a critical hit, for example.

Poison (and related effects)

For Injury-type poisons, the rules given in the DMG (p.257) are pretty clear about whether the poison is part of the attack's damage roll:

A creature that takes piercing or slashing damage from an object coated with the poison is exposed to its effects.

Taking damage only happens after you've already rolled the damage roll for the attack, adjusted it, and figured out what the target is actually going to take. That damage is the trigger for exposure to the poison, after which "a creature subjected to the poison" (common language used in all the poison descriptions) must make a save, and in many cases takes damage on a failure (and sometimes a lesser effect even on a success).

Here, you don't even know if the target needs to roll a save until you know if you did any damage. Your target might secretly be a werewolf and immune to the piercing damage from your non-magical non-silver dagger. You might be fighting a guy with the Heavy Armor Mastery feat and really flub your damage roll so that you didn't even scratch him. No injury, no injury poison.

Now, some add-on effects that include a save aren't based on actually taking damage, just being hit by the attack, like contact poisons or certain magical abilities. I would still say those damage rolls are a whole separate thing, though; again, the effect is brought about by failing a saving throw, not from being hit by the attack roll.

The most common place to see this is in venomous monsters. The scorpion's sting, for instance, seems to require you to make the poison save even if you nullify the 1 damage from its initial attack (such as if you have the Heavy Armor Mastery feat or resistance to piercing damage, since resistance means you halve the 1 damage and then round down to 0). I would say a DM should rule that it doesn't work that way, but in any case: The damage from the poison comes from failing a saving throw, not from being hit by the attack, so it shouldn't count as part of the damage roll for the attack. As an odd consequence of this, a scorpion that crits you doesn't deal any extra damage; the initial 1 damage doesn't have a die associated with it, so there's no roll to double, and the poison is a separate damage roll based on a saving throw, so it doesn't get doubled either.

Note that some dangerous monsters don't work that way. For example, the Basilisk just deals "2d6+3 piercing damage plus 2d6 poison damage" with its bite -- the poison is not a separate save; it seems to be an innate part of the attack's damage, so it's part of the single damage roll, the same as if you had a flaming sword.

When does the damage minimum apply?

As you quoted, the rule is "with a penalty, it is possible to deal 0 damage, but never negative damage". Damage dealt is at the end, the actual number you're going to subtract from the target's HP total. The minimum, therefore, applies at the very end of the process -- after every adjustment has been done and you're ready to change the target's HP, you just make sure you aren't about to do something silly like add HP because you somehow dealt less than no damage.

Answer 3

A damage roll is a roll of damage dice resulting from a weapon attack, spell, or monster ability (plus any bonus dice).

From the rules you quoted (emphasis mine):

Each weapon, spell, and harmful monster ability specifies the damage it deals. You roll the damage die or dice, add any modifiers, and apply the damage to your target. Magic weapons, special abilities, and other factors can grant a bonus to damage.

Note that in the initial listing, we have weapons, spells, and harmful monster abilities—the last not being a problem for PCs. This covers the weapon (club). One might argue the spell, too—see later. The last sentence lists examples which cover the rest of your situation—all of which apply to the weapon attack: a magic weapon (+1 club), special abilities (Sneak Attack), and other factors (Serpent Venom¹, Combat Inspiration).

The only arguable grey area would be the damage from hex, which, while being a spell which has a damage die associated with it, causes attacks to deal an extra d6 of damage. Seeing as this is almost identical phrasing to other 'special abilities' which are adding damage to the weapon attack, such as Sneak Attack, the most consistent interpretation would be to treat hex as a special ability, rather than a spell which itself deals damage.

For the purposes of the minimum damage rule, then, we would then have that all damage from the given example attack is one 'damage roll', and is bounded below in its entirety. For your latter example, this unfortunately means that the poor weedy creature deals 2 damage total, not 3. To answer your question:

The minimum is applied separately to the total damage resulting from weapon attacks, spells, and monster abilities.

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¹ As covered well in Darth Pseudonym's answer, there's a good case for poison (and similar effects) to be treated separately to the attack. Refer to his answer for the details, but I think he's right in his reading.

Answer 4

A damage roll determines how much damage you deal with an attack. Damage rolls vary widely with the different powers and weapons that can be involved, but the basic formula is often the same. If you're using a weapon for the attack, the damage is often some multiple of your weapon damage dice.