I know that if a caster casts and a spell as a Readied Action, they technically cast the spell on their turn and hold the spell until they use a ReAction to finish it. This means if they take damage they need to make a Concentration check to not lose the spell.
My question is this:
If a say, character with a ranged weapon Readies an Action to attack the first person who cast a spell, would the caster need to check concentration to not lose the spell being cast even if it's an Instantaneous spell?
I don't think 5e specifically calls this out as an example, the way 3.5 did, but spells don't give AoOs anymore either.
Example a group with a Ranger is fighting an enemy Wizard. The Ranger wins initiative over the Wizard. The Ranger Readies his action to shoot the Wizard if someone casts a spell. Wizard casts a spell (we'll say Fireball in the example). The Ranger sees a spell is being cast, uses his ReAction to shoot the Wizard.
since the Wizard has not finished casting the spell would the Wizard need a concentration check, even though it's not a Concentration spell, DC:10/half damage taken.
Admittedly, someone could possibly Ready an attack for "when someone starts casting a spell", or even "when the wizard puts his hand on his component pouch", or other things that would potentially place the attack after the spellcasting started but before it finished.
However, regardless of the timing, there is one specific rule to consider: Concentration can be broken by damage; there is no rule that says casting can. If you are currently holding Concentration, and you are dealt damage, you need to check if you hold it. Someone attacking you in the middle of casting doesn't interrupt you.
As such, it's actually a better idea to go with a trigger of "casts a spell" for Ready actions - it won't interrupt a non-Concentration spell, but it has a chance of interrupting a Concentration one. Attacking in the middle of the casting doesn't interrupt anything* (an spell doesn't require the caster's Concentration until it is successfully cast.)
*: Unless the caster is already concentrating, of course... >.>
XGtE p.5 cleared the rules for reaction timings up. It happens after the trigger completes, unless the reaction specifically states an exception. Attacks of Opportunity are one such exception, in that they happen before the trigger (moving away) completes.
RAW, only concentration spells and spells with a casting time longer than one action can be interrupted by damage. When you ready an action to cast a spell, you use the spell slot and begin concentrating on it (dropping whatever else you might be concentrating on), until after the trigger happens. You then cast the spell. Anywhere in between those two events, you have to make concentration checks if you take damage, and you drop the spell if you fail one.
When it comes to readying an action to interrupt a concentration spell with the casting time of one action (or bonus/reaction), while it is being cast, but before it completes...I'm not sure the rules even allow such a granular approach to events. My guess would be that the spell is uninterruptible before it finishes casting, unless a specific rule (like Counterspell's spelltext) overrules the general rule (or lack thereof).
I know that if a caster casts and a spell as a Readied Action, they technically cast the spell on their turn and hold the spell until they use a ReAction to finish it.
This means if they take damage they need to make a Concentration check to not lose the spell.
My question is this:
If a say, character with a ranged weapon Readies an Action to attack the first person who cast a spell, would the caster need to check concentration to not lose the spell being cast even if it's an Instantaneous spell?
I don't think 5e specifically calls this out as an example, the way 3.5 did, but spells don't give AoOs anymore either.
Example a group with a Ranger is fighting an enemy Wizard. The Ranger wins initiative over the Wizard.
The Ranger Readies his action to shoot the Wizard if someone casts a spell.
Wizard casts a spell (we'll say Fireball in the example). The Ranger sees a spell is being cast, uses his ReAction to shoot the Wizard.
since the Wizard has not finished casting the spell would the Wizard need a concentration check, even though it's not a Concentration spell, DC:10/half damage taken.
Following the rule from the DMG, the reaction happens after the trigger. In your case, the ranger can shoot after the wizard casts thespell.
As per Filcat.
Admittedly, someone could possibly Ready an attack for "when someone starts casting a spell", or even "when the wizard puts his hand on his component pouch", or other things that would potentially place the attack after the spellcasting started but before it finished.
However, regardless of the timing, there is one specific rule to consider: Concentration can be broken by damage; there is no rule that says casting can. If you are currently holding Concentration, and you are dealt damage, you need to check if you hold it. Someone attacking you in the middle of casting doesn't interrupt you.
As such, it's actually a better idea to go with a trigger of "casts a spell" for Ready actions - it won't interrupt a non-Concentration spell, but it has a chance of interrupting a Concentration one. Attacking in the middle of the casting doesn't interrupt anything* (an spell doesn't require the caster's Concentration until it is successfully cast.)
*: Unless the caster is already concentrating, of course... >.>
XGtE p.5 cleared the rules for reaction timings up. It happens after the trigger completes, unless the reaction specifically states an exception. Attacks of Opportunity are one such exception, in that they happen before the trigger (moving away) completes.
RAW, only concentration spells and spells with a casting time longer than one action can be interrupted by damage. When you ready an action to cast a spell, you use the spell slot and begin concentrating on it (dropping whatever else you might be concentrating on), until after the trigger happens. You then cast the spell. Anywhere in between those two events, you have to make concentration checks if you take damage, and you drop the spell if you fail one.
When it comes to readying an action to interrupt a concentration spell with the casting time of one action (or bonus/reaction), while it is being cast, but before it completes...I'm not sure the rules even allow such a granular approach to events. My guess would be that the spell is uninterruptible before it finishes casting, unless a specific rule (like Counterspell's spelltext) overrules the general rule (or lack thereof).
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