I’ve been thinking of fighter maneuvers for a while now, but here’s another!
Mage Hammer. When you hit a creature with a weapon attack, you may expend a superiority die to cause a spell caster to have to make Constitution saving throws when casting any spells for a number of turns equal to the number rolled on your superiority die. On a failure the spell slot is lost to no effect. If the spell was a cantrip, the character simply fails to cast the spell.