Set sometime post season 2 after Foggy and Matt go their separate ways. The next big bad somehow clues into Daredevil relying on his other senses to do what he does and finds a way to permanently limit or damage them. Maybe they remove an eardrum, resulting in permanent hearing loss and issues of vertigo. (Would prefer if he's not rendered fully deaf). Or something else entirely as long as it effectively ruins Daredevil's career and (arguably) Matt's life.

After awhile, Foggy learns through Brett or Karen or Facebook (lol) that Daredevil has retired and he's happy about it... until he finally runs into Matt and realises exactly why Matt's called it quits. Cue moral dilemma about being relieved Matt's just a "normal" blind man and no longer risking his life as the man in the mask.

Alternatively, it doesn't have to be permanent damage. I'm just here for Matt whump with a conflicted Foggy... little to no c with my h just fuck me up :)