Can you counterspell a spell if you don't know who's casting it?

Question

Related to this question about a spellcaster hiding in a group of spellcasters.

The reaction trigger for counterspell is "when you see a creature within 60 feet of you casting a spell". It has a range, but no target.

Suppose the Death Eaters all start chanting and waving their wands at once, and I can't tell which of them is really casting the spell. But one of them is a creature casting a spell within 60 feet, and I do see it (because I see them all). Can I counterspell "whoever", or do I have to aim for one of them specifically?

(If you want mechanical details, assume all but one of the mages readied this action: "When any other Death Eater chants and waves their wand, chant and wave my wand." Then one of them started casting a V, S, M spell. Also assume the whole thing isn't a bluff, which would be a different scenario.)

Answer 1

It depends - is magic obvious or not?

I haven't found anything in the rulebooks to explicitly say it, but it reads to me that casting a spell is obvious. An observer can always tell the difference between someone waving their hands and speaking nonsense, and someone casting a spell.

If it is obvious

"Suppose the Death Eaters all start chanting and waving their wands at once…"

The one Death Eater casting will stand out from the rest. To steal a line from my favourite kids tv show, "One of these things is not like the others."

If it is not obvious

Then counterspell is useless. Swap it for another spell.

Seriously, if magic is not obvious then there is no need to fake anything (and thus no Deception roll needed) - just wave your hands and speak gibberish before and after the casting spell. Observers have no way to tell which is gibberish and which is actual spellcasting, so the couterspeller has to guess at which point in time you start casting the spell.

Player: My sorcerer waves their hands. Any counterspell? No, ok, they wave their hands a bit more. Counterspell? Ok, no, so they do a bit more waving. Counterspell? No? PSYCH! that was the actual spell, the fireball goes off.

I suspect rules interactions like this are why spellcasting is usually considered to be obvious.

Answer 2

Counterspell has a target

You attempt to interrupt a creature in the process of casting a spell.

If only one of the Death Eaters is actually casting a spell and the others just “chant and wave my wand” there is only one creature casting a spell so only one valid target. If the counterspeller can see that target, they can Counterspell. The rules for targeting are:

A typical spell requires you to pick one or more targets to be affected by the spell's magic. ("The creature casting the spell")

Beyond that, all that is required is a clear path and, for this particular spell, that you can see the caster. The fact that you can also see other creatures who are not casting a spell is irrelevant.

Alternatively, if all of the Death Eaters are actually casting a spell then they don’t do it at the same time. Obviously, if they each take the Cast a Spell action they will do it sequentially on each of their turns and the Counterspeller will have to decide to Counterspell or not as each trigger happens.

The same is true if each Death Eater takes the Ready action because:

When you ready a spell, you cast it as normal but hold its energy ...

The time for Counterspell is when the spell is “cast ... as normal”.

Answer 3

According to the Counterspell text, the Casting Time is "1 reaction,...

...which you take when you see a creature within 60 feet of you casting a spell.

In 5e, because of the importance of the action economy, reactions are very strict, and are only allowed under very specific circumstances, as written. In this case, you must see a creature that is casting a spell.

There are several indications in the rule books that spellcasting in and of itself does not present any visible signs in the absence of verbal and somatic components. The sorceror metamagic ability Subtle Spell (PHB p.102) says:

When you cast a spell, you can spend 1 sorcery point to cast it without any somatic or verbal components.

If spellcasting activity was innately identifiable despite the absence of these components, then this particular ability wouldn't be very subtle, would it?

Also, in the Spellcasting chapter of the PHB (p. 204) under Targets, we have:

Unless a spell has a perceptible effect, a creature might not know it was targeted by a spell at all. An effect like crackling lightning is obvious, but a more subtle effect, such as an attempt to read a creature's thoughts, typically goes unnoticed, unless a spell says otherwise.

Lastly, according to the Sage Advice Compendium,

If a spell that’s altered by Subtle Spell has no material component, then it’s impossible for anyone to perceive the spell being cast. So, since you can’t see the casting, counterspell is of no use.

So, you must perceive the spellcasting activity. However, since the visible components of spellcasting appear to only be the somatic components themselves (barring any visible effects like a fireball), there is no indication I have found in the rules that there would be any way to distinguish between the caster and someone who cannot cast the spell making the same noises and hand gestures.

By this argument, the OP's question makes sense. It is possible to see someone casting a spell, but not know whether they are actually casting or just acting. That means the real question is

...do I have to aim for one of them specifically?

The spell doesn't use the word "target". However, the first line of the spell says:

You attempt to interrupt a creature in the process of casting a spell.

Since the spell only affects 1 spell being cast, and not an area, it seems straightforward that you would have to specify the creature you intend to interrupt.

So yes, you have to choose.

Now, having said that, if the other creatures aren't casting the same spell but are just acting then, as a DM, I would have them make a deception check to get the moves right to fool you. And that would be easier if you didn't know anything about spellcasting, so the obvious opposing skill roll I would ask for from you would be an Arcana check. If you don't have that skill, I might allow Perception to figure out if one or more of these fellows seem more adept than the others in their movements. Depending on the relative die rolls, you might eliminate some or all of the imposters from contention and improve your odds.

Answer 4

I will assume that the Death Eaters have a strong enough grasp of magic to make a compelling attempt at mock spell casting.

The DM must decide if the Death Eater that is truly casting is discernible from the others at all through a relevant check; be it Arcana, Insight or maybe just Perception and if the Death Eaters are using their action in this way they are now contesting it with their own Deception, Arcana or even Performance check. The ones that create a compelling enough show are now targets that are treated as casting that the Counter Spelling creature must choose from.

For those Death Eaters with an indiscernible fake casting then the creature casting counter spell interprets several Death Eaters all casting at once and must either choose one or have the dice decide.

How many Death Eaters are faux casting and put up a compelling enough performance? 5 "realistic" fakes and 1 real? Roll a d6.

There is the possibility that a simultaneous chorus of chanting creates a cacophony of noise that adequately masks the caster and there is no time to apply a discerning eye and just try using counter spell on one and hope for the best.

In which the same applies with no check. Just a choice or a dice roll. There are after all a number of Death Eaters spending their action and reaction to ready their performance/deception/arcana check to protect the action of one.

If the caster of counter spell fails to choose the appropriate target the counter spell fails.

Answer 5

You can counterspell it

The rules are clear: "when you see a creature within 60 feet of you casting a spell". Someone who is pretending to cast a spell is not casting a spell. There is no confusion.

You do not need to observe verbal or somatic components to counter a spell

You have assumed that counterspell has something to do with sight, but that is not true. Only the trigger requires you to see someone casting a spell, but there isn't anything in the skill that actually says that.

A sorcerer can use metamagic to cast a spell with no vocal or somatic components:

Subtle Spell

When you cast a spell, you can spend 1 sorcery point to cast it without any somatic or verbal components.

This spell can still be counter spelled. Mechanically you do not have to explain how you are identifying who casts the spell, it is assumed that you can do this automatically.

You can explain this as detecting magical flux or whatever you want, by the rules it doesn't matter.

But if a PC wanted to do this, I may allow a deception check

A reasonable way that a DM could make this situation interesting is by using deception to have the casters hide who is casting the spell.

Answer 6

There is a huge mistake here. Counterspell doesn't say it counters a completed spell, it doesn't say it counters a spell being cast by a creature, it says "when you see a creature within 60 feet of you casting a spell". It is 100% based on assumption, otherwise it is metagaming to know 100% if a spell is being cast or not. A spell requires 0-3 components, unless metamagic or something else is applied, those components are all required for a given spell, and a spell has a level but can be upcast to a higher level. This cause numerous factors that either require metagaming to know, or require that Counterspell is based on Assumption, not truth.

Material Components:
You see someone pull out a mix of Sulfur, Charcoal, and Bat Guano... are they Fighter about to pack their pistol with gunpowder or a Wizard about to cast Fireball? You can Counterspell, but you are using the slot, either way.

Somatic Components:
You see a Thri-Kreen making gestures for Dominate Monster, they know the exact gestures, it is an 8th Level Spell, you will need to upcast counterspell to 8th or 9th level to counter it... but since you don't speak Thri-Kreen, all you hear are clicks, whistles, and chirps, they could be literally saying "Counter this Dummy", and not have the slots or any intention of dominating the huge monster you have with you... If YOU don't know for sure, you can always expend the slot, it is like holding an action, the slot is used, whether or not the actual trigger is valid.

Verbal Components:
A Paladin shouts the verbal components to Fear, taught to them by the Wizard, while activating their Paladin Feature, the fear works, even if you cast counterspell, but you saw they cast it, you did, because it only has a verbal component, and magic did trigger, so it has nothing to do with magic. Counterspell is an interruption as a reaction, it is meant to prevent the completion, not stop a spell that has already been cast, you stop it in its tracks or you don't.

Other Tricks:
Major Image, once cast allows the Bard to hold his action every turn to create an army of copies of the Wizard or Warlock all casting various spells, the gestures are accurate, the verbal components sound accurate, the material components appear accurate, that is a dozen spellcasters, all accurately casting real spells (because if you don't know they're an illusion, you will feel the effects of all the spells, not just the real one, and worse, your counterspell fails on all of them anyway), so your reaction has a dozen valid triggers, except none of them is actually a real spell, despite all of them about to feel totally real when they hit you, and kill you...

Fist:
Muscle Wizard Casts Fist, you cast Counterspell, the Fist Spell countered your Counterspell, because Counterspell is useless against the Fist Spell of a properly experienced Muscle Wizard. Never be in range of Fist with a Counterspell, you will lose most of the time.

People need to grasp the concept that You can always waste a spell slot, it is a built in mechanic, it is why spellcasters are best choosing cantrips for all held actions, because otherwise if a trigger never happens you have squandered the slot, Counterspell is no different, you react. You can cast Shield when an Opponent rolls a 1, you shouldn't, but you can... likewise, you can cast Counterspell at a Barbarian 70' away that was taught how to imitate the exact gestures and words of Eldritch Blast by the Warlock for when the Barbarian is still too far to attack, it will succeed, the Eldritch Blast will never go off (not that it would anyway, but YOU SAW A SPELL BEING CAST AND CAST COUNTERSPELL TO COUNTER IT, nowhere does it say "When you see a SPELLCASTER casting a spell", it says when you see a creature casting a spell, not cast, casting, it means you have to see it and you choose to react).

Always remember, you can waste actions, it is Metagaming to know truth from misdirection without a role. YOU Roll, it is your perception, not their deception, unless they have no ideas at all. Yes, if the Barbarian starts mumbling and waggling his fingers because he thinks that is how spells work, it is an opposed check (hey, he could be lucky, and his mumbling could sound like Power Word Kill for all you know), your DM can then choose to have you roll Insight (to tell that the Barbarian is just pretending) or Arcana (cause he just got lucky and is on a leyline, and is about to cast a Level 9 Spell by pure dumb luck (hope for the insight check, seriously, you don't want to waste a level 9 spell on countering a Barbarian casting a spell, but you definitely don't want to not counter a level 9 Power Word Kill).

Answer 7

You will know who is casting a spell.

Waving your hands around and chanting gibberish can't be confused with spellcasting.

Consider the Flameskull. It can innately cast spells, and doesn't need to use either verbal or somatic components to do so. The innate spellcasting abilities of monsters are subject to counterspell according to an unofficial tweet by Mike Mearls. Nothing in the Flameskull's stat block suggests that its spells can't be counterspelled due to a lack of verbal or somatic components, so there must be some other component of a spell being cast that can be detected.