Can you use Shield as a reaction against the damage from Fire Form?

Question

This issue came up in a recent session:

A character used Shocking Grasp against a Fire Elemental. Due to the Fire Elemental's ability Fire Form, the attacking Character took damage. Can they use Shield as a reaction against the damage from Fire Form?

Pretty new to D&D5e, I've been playing 3.0/.5 for about 25 years. I have some savvy players, and this came up. I ruled it was fine until I figured it out. Though, I believed the PC was not attacked by the monster, so you shouldn't be able to spend the spell slot.

Answer 1

Shield cannot be used as a reaction to damage

5th edition generally does a good job choosing language that deliberately interacts with other language (especially for the "core" set of rules: Monster Manual, Players Handbook, and Dungeon Masters Guide).

So, let's take another look at the abilities in question:

Fire Form
...[snip] A creature that touches the elemental or hits it with a melee attack while within 5 feet of it takes 5 (1d10) fire damage [snip]...

and

Shield
...[snip] Casting Time: 1 reaction, which you take when you are hit by an attack [snip]...

Shield can only be used against attacks (or Magic Missile), and the damage from Fire Form is not an attack (nor is it Magic Missile). There's no roll or targeting, it just happens.

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Worth noting: not all reaction spells are the same.

Some reaction spells would qualify against Fire Form.

For example, Absorb Elements grants you resistance against the element that damages you and lets you deal damage of that type, while Hellish Rebuke deals fire damage against creatures that damage you; though, in both cases against a Fire Elemental, they'd deal fire damage, which isn't super helpful.

Answer 2

The relevant portion of Fire Form reads (from DnD Beyond):

A creature that touches the elemental or hits it with a melee attack while within 5 feet of it takes 5 (1d10) fire damage.

Shield's trigger is (again, DnD Beyond):

which you take when you are hit by an attack or targeted by the magic missile spell

The character wasn't targeted by an attack, and cannot cast shield.

Also important to note, shield wouldn't help anyway, since Fire Form doesn't care about AC and isn't a magic missile spell.

Answer 3

Shield doesn't protect against you sticking your hand into fire.

What Shield gives you (besides stopping magic missiles) is a +5 bonus to AC, which is the same benefit you'd get from 3/4 cover.* It's best understood as a kind of temporary partial cover, in that it reduces the chance of an attack hitting you.

Shocking Grasp is a melee attack; the spell description says that the lightning comes from your hand. So you're touching (or nearly touching) a fire elemental with your hand. The elemental isn't attacking you and possibly hitting your cover; you are initiating contact with it and getting burned.

Mechanically, this is represented with Fire Form not needing an attack roll, and thus not being stopped by your +5 AC.

*With the slight wrinkle that it stacks with any real cover you have. Normally you can't get above +5 with cover; the next step is total cover, which makes you impossible to hit.