Counter Spell?

if you are within 5 feet of a creature, who is casting a spell, you can use your reaction to make an unarmed strike. If you successfully hit the target with the unarmed strike, the caster must make a concentration check to be able to cast the spell.

you get +5 to hit when using this effect and if the target does not know you are there, the concentration check is made with disadvantage.

A town of daddly fighters knew "exactly" how to cast counter spell.