If somebody Counterspells a Counterspell, is the original spell cast successfully?

Question

Assume Caster A casts fireball.

Assume Caster B casts counterspell on A's fireball using his reaction.

Now Caster A can use his reaction and also cast counterspell on Caster B's counterspell.

Does this mean that Caster A can finally cast fireball and B can do nothing about it?

Or does this mean that Caster B can cast another counterspell to counter Caster A's counterspell attempt?

This gets out of hand so I described it as simple as I could. I hope I get an answer because I was on a dispute with one of my players for this mechanic.

Answer 1

Yes, the original spell will take effect

Counterspell has no restrictions on what spell it can counter (beyond the possible ability check for higher level spells).

It states that the...

spell fails and has no effect.

So if a Counterspell is, in turn, countered, it will have no effect.

If that Counterspell has no effect then it was not able to counter the original spell!

With only two casters this is as far as it can possibly go of course, because each caster only has 1 reaction. More casters = more possible reactions so it could indeed get very silly, though in practice it seems doubtful you would have so many casters about who also have that spell prepared!

Answer 2

Yes, provided you have a Reaction available.

The Counterspell description says (emphasis mine)

You attempt to interrupt a creature in the process of casting a spell. If the creature is casting a spell of 3rd level or lower, its spell fails and has no effect. If it is casting a spell of 4th level or higher, make an ability check using your spellcasting ability. The DC equals 10 + the spell's level. On a success, the creature's spell fails and has no effect.

Under "Casting Time", the PHB (pag 202) says (emphasis mine)

Some spells can be cast as reactions. These spells take a fraction of a second to bring about and are cast in response to some event.

Hence, the steps are the following:

• Caster A casts a spell.
• While A is doing the magic (moving hands, chanting, et cetera), caster B casts Counterspell. Suppose that B has success.
• Two possible interpretation may arise:
  1. A can "pause" its casting to use its Reaction (if available) in the middle of casting a spell and cast Counterspell too, to contrast B's. In case of success, A resumes to cast its spell which has normal effect.
  2. Casting a spell does not allow any "pausing", hence there is no way that A succeeds in casting its spell.

The first interpretation satisfies the description of Reaction casting time: by RAW and moreover under what it is written in the latest version of the Sage Advice (pag 14, Can you cast a reaction spell on your turn?) you can use Counterspell as a response (reaction) to a Counterspell of another caster while you are casting a spell. The second interpretation is in contrast with the first one: hence it is not valid.

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Or does this mean that Caster B can cast another counterspell to counter Caster A's counterspell attempt?: No, because B has only 1 reaction per turn that had already been used for casting the first Counterspell.

If there would be a 3rd caster C, then C can cast Counterspell on B's Counterspell, allowing A's Fireball to be activated, without A being forced to use another 3rd (or higher) spell slot.

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Under a role-play point of view, we can see the Counterspell as just one (or more) gesture(s) that ruins the manipulation of the Wave by a caster. Using Counterspell against another Counterspell during a spell casting is possible (just add a simple gesture to the casting), and it can be seen as the two casters battling for mastering the Wave.

Answer 3

PJRZ's answer is correct per rules as written. The exact exchange of spells described here is specifically cited as a legal example in the Sage Advice Compendium.

I assert that the rules as written are bad and wrong.

The legal target of Counterspell is "a creature in the process of Casting a Spell." The original caster has not finished casting the original spell when the counter caster starts casting Counterspell, or they would not be a legal target. In order for the original caster to cast Counterspell on the Counterspell, therefore, one of the following must be true:

1. You can be casting two spells at the same time.
2. You can stop the process of casting a spell, do something else, and then resume and successfully complete the casting.

I assert that both of these are inconsistent with the image of spellcasting produced by the rest of the rules text.

1. Spells have casting times, as well as verbal, somatic, and material components unique to the spell. The rules are generally explicit about which things you can do at the same time, and there is no indication that spells are an exception.
2. The rules on spells with a casting time of more than one turn state:

   When you Cast a Spell with a Casting Time longer than a single action or Reaction, you must spend your action each turn casting the spell [...] If you want to try casting the spell again, you must start over.

Counter-countering does violence to the imagination in much the same way that the peasant railgun does, and that is reason enough for me to suggest excluding it, the rules authors notwithstanding.