Does a multiattack count as a single source of damage?

Question

The rules for maintaining concentration on spells after getting hit state that:

If you take damage from multiple sources, such as an arrow and a dragon’s breath, you make a separate saving throw for each source of damage.

This is an example for two very distinct sources of damage.

If a character who is concentrating on a spell gets hit by a creature with the multiattack feature, do they have to try to maintain concentration for each time they were hit? Or only one time, since technically all of the attacks came from the same source?

Answer 1

A concentration check is needed for each hit

A multiattack is separate attacks, so you'd have to roll for each attack that hits. The reason the PHB uses "sources of damage" instead of "each time hit" is because some damage sources use a saving throw instead of an attack roll, or automatically cause damage. So you need to make a concentration check, for each instance of damage taken.

Examples

• Scorching Ray - You create three rays of fire and hurl them at targets within range. You can hurl them at one target or several. Make a ranged spell attack for each ray. On a hit, the target takes 2d6 fire damage. Each ray is a separate attack, and requires a separate concentration check.

• Sword of Lightning - 1d8 slashing + 1d4 lightning damage. Two damage types, but one source (the sword attack); one concentration check.

• Dragon - Wing Attack [...] Each creature within 15 feet of the dragon must succeed on a DC 23 Dexterity saving throw or take 15 (2d6 + 8) bludgeoning damage and be knocked prone. One source of damage. One concentration check on a failed save.

Edge Case

• Imp - Sting [...] Hit: 5 (1d4 + 3) piercing damage, and the target must make on a DC 11 Constitution saving throw, taking 10 (3d6) poison damage on a failed save, or half as much damage on a successful one. By RAW, one hit and one save, thus two concentration checks; however, it can be easily argued for a house ruling that it is one damage source since the save only determines the amount of poison damage not whether there is poison damage.

• Magic Missile - Multiple darts that hit simultaneously. Since the darts automatically hit, there is no attack roll nor saving throw. Thus, ambiguous as to whether it is one damage source or multiple. There are valid arguments for ruling both ways. However, Jeremy Crawford rules that each dart requires a separate concentration check. As a lead designer, his tweets can be considered RAW.

Answer 2

No

Make a concentration check for each instance of damage taken from attacks or spells:

Do you roll concentration for every instance of damage taken? id est every Magic Missile hit?

Concentration: "You make a separate saving throw for each source of damage" (PH, 203). Roll for each missile.

https://twitter.com/JeremyECrawford/status/716012166101401600

The PHB means a mechanical "source of damage" (the damage roll), not an in-world source of damage like "weapon", "enemy", etc.

technically all of the attacks came from the same source

If this was true, you'd roll only once for all similar attacks from this enemy. However, you are supposed to roll for its every attack. Keep in mind a Multiattack can also be interrupted by movement, these attacks can be made against different enemies, etc.