Altheus's Timeout Variant

It's quite rude to interrupt someone while they are speaking. Let the grown-ups talk for once please.
- Arcane Scribe, Altheus Alvago

You interrupt a creature in the process of casting a countering spell. If the creature is a spell with a reaction casting time, the spell fails unless it is cast at 5th level or higher. Then, you must make a saving throw using your spellcasting ability with a DC of 10 + the spell's level. On a failure, the countered spell does fail, but you instantly lose concentration on it. On a success, this spell works as normal.

After countering the spell, the inital spellcaster cannot cast spells using their reaction as long as you maintain concentration.

At Higher Levels. If this spell is cast at 6th level you may make it so the spellcaster cannot cast spells using their bonus action instead of their reaction, and at 8th level you make it so the spellcaster cannot cast spells using their action instead of their reaction.