So, we have a Tiefling Barbarian in our campaign, who just gained access to Hellish Rebuke as a racial spell. The spell states that you point at a target that has attacked you, and they catch fire.
Typically, you cannot cast spells while enraged, but this is a reaction, and has no "memorized" or "hand sign" components; can this racial spell be cast while raging?
The rules are quite clear (emphasis mine):
Rage
[...] If you are able to cast spells, you can't cast them or concentrate on them while raging. [...]
&
Infernal Legacy.
[...] you can cast the hellish rebuke spell [...]
So by the rules, you are not able to cast any spells independent on what kind of action and components they need as long as you are raging.
Casting Hellish Rebuke when raging is not possible.
If you are able to cast spells, you can't cast them or concentrate on them while raging. (Player's Handbook, page 48, under Rage)
The casting time or source of the spell doesn't have an impact here - a raging barbarian simply can't cast spells at all.
No, they cannot cast the spell
From the Barbarian class feature Rage..
... If you are able to cast spells, you can't cast them or concentrate on them while raging.
