This Is a homebrew creation for a subclass that is dedicated to fighting mages

Level 3: Sprung Trap

You gain 5ft of movement speed and you have advantage on Initiative Rolls.

Level 3: Strength Against Magic

When you deal damage to someone who is concentrating on a spell, add your proficiency to the resulting concentration check dc.
Also you can sense when someone within 5ft of you is concentrating on a spell.

Level 7: Protective Insight

As a Bonus action you can provide insight to ally's nearby to help protect them from incoming spells

This gives you and ally's within 5ft of you or ally's within 5ft of a large or smaller creature you are within 5ft of a benefit of Plus Proficiency to their save against any spell Until the start of your next turn.

At Level 10 this Aura extends to 10ft Around you, this dosent scale the second part, The Max creature size increases to Huge

At Level 15 This Aura Extends to 15ft Around you, this dosent scale the second part, The Max creature size increases to Gargantuan.

Level 10: Reactionary Spell Breaker

As a reaction whenever a creature within melee range casts a spell, you may make an attack against that creature if it hits, this causes the creature to make a concentration check if the caster fails the spell is considered countered. (this does not stop ongoing concentrations) You can do this twice per long rest. This Increases to 3 times at level 14 and to 4 times at level 17.
You can also use this to make a reaction attack against a creature within melee range that made an melee attack, there is no additional effect.

Level 15: Never Go Alone

When you use your Action Surge feature, you can choose Two creatures within 30 feet of you that is allied with you. That creature can make one melee or ranged weapon attack with its reaction, provided that it can see and hear you.

Level 18: Mana Purge

You Gain 2 Uses of this which recharges on a long rest.
As an action you may make one melee attack against a creature within melee range if this attack hits, that caster losses all spell slots of the lowest level that is still useable.
(example if you hit a caster who was used all his 1st level spells, they will lose all available 2nd level slots)