A fighter that first and foremost is built to bast casters.

Unspelled

You have Advantage on Saving Throws against Spells and other magical effects, and Spell Attacks have Disadvantage against you.

Component Crush

Up to a number of times per Short Rest equal to your Proficiency Bonus, on a successful hit against a target, you can choose to forgo damage and in exchange do a one of the following;

Try to knock a single object that they are holding out of their hand, failing if the target succeeds on a Strength Check, DC equal to 8+twice your Proficiency Bonus

Strike at their throat or nearest equivalent, causing them to only be able to speak faulteringly for 1d4 rounds and having to succeed on a Save using their Spellcasting Stat to cast a Spell with a Verbal Component, DC of 8+your Proficiency Bonus

Partly disable one of their arms for 2d4 rounds, making that arm lack the needed range of motion to perform the Somatic components of spells that require any.

Magical Resistance

At 10th level, you have Resistance to damage from Spells and other magical effects.

No Spell

A number of times equal to twice your Proficiency Bonus per Long Rest, as a Reaction when you would be directly affected by a Spell or other magical effect, you can choose to not be.

Magic Averse

You are able to exude a powerful aura of magic ruining around you.

Once per Long Rest, as an Action, you can radiate Antimagic, as if the Antimagic Field spell, affecting a fifteen foot radius around you, and for a further fifteen feet beyond that exude a Wild Magic Field, same effects as being within a Wild Magic Field, for a number of rounds equal to your lowest Ability Modifier between Int, Wis, and Cha.