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Scenario: Rogue is hidden and sneaks up on a Wizard. Rogue attacks and hits the wizard with 1 above his AC. Can the wizard take his reaction to Shield from it?

Shield's casting time is 1 reaction, which you take when you are hit by an attack or targeted by the Magic Missile spell.

Until the start of your next turn, you have a +5 bonus to AC, including against the triggering attack, and you take no damage from magic missile."

The wizard is arguing that the RAW is any attack that hits him. The Rogue is stating that he's hidden and that the wizard shouldn't be able to see it coming. To this the wizard argues that when you attack you lose your stealth and gives enough time to activate a reaction.

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  • \$\begingroup\$ Did either of the players read the rules, specifically the text of the shield spell? \$\endgroup\$ – KorvinStarmast Apr 19 '17 at 20:36
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You've already stated the key point:

1 reaction, which you take when you are hit by an attack or targeted by the magic missile spell.

So what you need to understand here is that the Shield spell involves time travel. No, really, it does. You can cast Shield when you're hit by an attack. Not when you're targeted, or when someone tries to attack you, but when you're hit.

The time travel shenanigans comes into play because the AC bonus of Shield applies to the attack that caused you to cast it. So stealth doesn't apply here, because when the Rogue stabbed the Wizard, it gave away his position. Then the Wizard changed history with the Shield spell.

See here for a similar explanation phrased a little differently. It's easy to understand how this works in terms of gameplay: wizard gets hit, wizard casts Shield, wizard does or doesn't get hit based on his new AC including Shield. How it works in-game is, well, magic! (Alternatively, if you prefer, A Wizard Did It.)

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    \$\begingroup\$ Ah! I found it, and I don't know how to comment it in: thesageadvice.wordpress.com/2014/10/11/shield-before Brail Says: Am I right..Wiz should know roll before using Shield,can't waste it from not knowing roll? Mike Mearls says: correct 6:02 PM - 8 Oct 2014 New to D&D and don't know who Mike is, but it says he's the lead designer of D&D or something along those lines. \$\endgroup\$ – Sedriel Spelloyal Dec 23 '14 at 6:57
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    \$\begingroup\$ No need to invoke time travel and obliterate Occam's razor. There are less extreme plausible explanations. Off the top of my head, in-fiction Shield could be a "latent" spell that is ready to trigger at the speed of magic (faster than thought). Another is that, as we all know, HP are an abstraction and aren't actual injury until you're quite low, so 1) the dagger "hits" in the not-actually-injuring way, 2) the wizard notices, 3) wizard brings Shield up to null the "bruising and fatigue" that most HP represent. No need to add amazing but ho-hum casual time travel not mentioned in the fluff. \$\endgroup\$ – SevenSidedDie Dec 23 '14 at 17:19
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    \$\begingroup\$ As far as the time-travel issue, it's a reaction to someone swinging. It's like an AoO, a parry/riposte, etc. It's a spell that can be used so quickly that it can effectively take an attack that was going to hit and turn it into a miss, creating a barrier around yourself to protect you for the round. It doesn't take time-travel to see an attack as it's coming in (unless it is during a surprise action, that's the point of surprise and ambush). It just takes combat and fast action to react in order to 'block'. \$\endgroup\$ – Aviose Dec 23 '14 at 19:41
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    \$\begingroup\$ This reply misses the fact that, if you are surprised, you cannot take a reaction until after your first turn in the combat. So if the rogue has initiative over the wizard, the wizard can't cast Shield as a reaction in the first turn of the combat. If the wizard wins initiative, then he can use Shield. I'm afraid it does not give the complete picture according to RAW and is misleading. @Erik has it right. \$\endgroup\$ – Clearly Toughpick Mar 23 '17 at 14:45
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    \$\begingroup\$ @ClearlyToughpick Surprise isn't part of the question. \$\endgroup\$ – Miniman Mar 23 '17 at 14:48
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Depending on the context of the encounter, the following quote from the PHB, page 189, might be relevant:

Surprise

If you're surprised, you can't move or take an action on your first turn of the combat, and you can't take a reaction until that turn ends.

So if the Rogue's sneaky stabby is the start of the combat and the Wizard wasn't expecting him, he isn't allowed to use his Reaction. But if it's the middle of a fight and the Wizard is already completely on edge and ready to cast, then he can do it.

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  • \$\begingroup\$ I can accept this.=D I think my question was more of a mid combat thing but I completely forgot about Surprise. Thanks. \$\endgroup\$ – Sedriel Spelloyal Dec 23 '14 at 17:28
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Ok, I think I've got enough to answer this.

If the scenario is before any combat has started the wizard failed his Perception check or otherwise didn't notice the Rogue in stealth, and was Surprised by the attack. The Wizard does not have a reaction to cast Shield with, due to the Surprise effects debuf.

However, if it's mid-combat and the same failed Perception happens. The Wizard has his reaction and can Shield from the blow. Provided that Shield will be enough.

Furthermore, the Wizard knows the roll that was made against his AC and can safely use Shield so that his spell slot will not be expended in a wasted effort. This can be seen by this twitter exchange with a D&D Developer. http://thesageadvice.wordpress.com/2014/10/11/shield-before/

Thanks guys!

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