The Defence fighting style reads:
While you are wearing armor, you gain a +1 bonus to AC
Is a shield considered armor for this purpose?
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Sign up to join this communityThe Defence fighting style reads:
While you are wearing armor, you gain a +1 bonus to AC
Is a shield considered armor for this purpose?
In the Monk Unarmored Defense section it is specified that
Beginning at 1st level, while you are wearing no armor and not wielding a shield...
and in the Barbarian Unarmored Defense
While you are not wearing any armor, your Armor Class equals 10 + your Dexterity modifier + your Constitution modifier. You can use a shield and still gain this benefit.
Which indicates armour and shields are considered separate.
Ultimately, due to some very unclear descriptions of armor and shields the most definitive verdict is from Jeremy Crawford, who tweeted:
Q: Does wielding a shield count as wearing armor [for the defense fighting style]?
A: No.
Which I think is a strong confirmation that unless specifically called out, shields do not count as armor in game terms, and were referred to as armor in a more plain English sense, mistakenly.
Shields are in the Equipment section (Chapter 5) of the PHB, but are not classified under the Armor section when determining Light, Medium, or Heavy Armor.
The posted Sage Advice also contains some details differentiating Shields from Armor:
These methods—along with any others that give you a formula for calculating your AC—are mutually exclusive; you can benefit from only one at a time.
…
What about a shield? A shield increases your AC by 2 while you use it…[k]eep in mind that some AC calculations, such as a monk’s Unarmored Defense, prohibit the use of a shield.
This was further clarified via Twitter by Jeremy Crawford
Does wielding a shield count as wearing armor [for Defense fighting style]?
Jeremy Crawford: No.
There is another complimentary Tweet from Jeremy Crawford that states the same:
The Defense fighting style is intended to work with a suit of armor you wear, not with a shield alone
If you look at Character Class options and review the listed Proficiencies, you'll notice something at odds with all of the above in my answer. As an example, let's look at the Fighter (PHB, 71).
Armor: All armor, shields
This does make it look like Shields are a subset of armor and would be permissible under the current written rules of the Defense Fighting Style. And, as @Goodguy5 answer states, it's not likely a huge issue for someone who invests in a 2 level dip to get the +1 AC who wields a shield without wearing armor.
*Big Thanks to @Christopher for their answer here in help supplying the content of this answer.
Jeremy Crawford has clarified:
Q: Does wielding a shield count as wearing armor [for the defense fighting style]?
A: No.
and again here:
The Defense fighting style is intended to work with a suit of armor you wear, not with a shield alone.
Considering that shields are not listed in the armor section in the PHB, but are instead listed in the equipment section, I'd say that it is clear that shields are not intended to be armor in the rules.
There is supporting evidence also in the description for a monk's unarmored defense ability:
Beginning at 1st level, while you are wearing no armor and not wielding a shield...
This ability makes clear that armor and shields are considered separate and distinct. The Sage Advice Compendium confirms and elaborates a bit about this:
Shields are grouped with armor in the equipment rules in the Player’s Handbook, but various game features distinguish between the armor you wear and a shield you wield. Take a look at the monk’s Unarmored Defense feature and compare it to the barbarian’s version. In the monk’s version, you must both forgo wearing armor and forgo wielding a shield if you want to benefit from the feature, whereas a barbarian must only forgo wearing armor. (Sage Advice Compendium p.16)
Taken together I seems clear that the interpretation above is pretty well supported by RAW as well even if it is not as explicit as it could/should be.
It's possible to make a call in your game (or request the GM to make a different call) based on what you're going for.
Personally (as a house rule), I'd update the phrasing to resemble something like: "While you are wearing armor or wielding a shield, you gain a +1 bonus to AC".
I can't think of a realistic scenario where I (as a GM) would be upset with the +1 ac you get. The obvious concerns are "Unarmored Defense" or "Mage Armor" or some such. But, if a character wants to take a one or two level dip to snag +1AC, so be it.