Fiction book where the main protagonist is a boxer, MMA athlete etc

I'll be honest and say this stemmed from watching Knives Out and being interested in Father Jud's background. Fanfics are out there but I'm not really a fan of those anymore hahaha…

It can be any genre, but I prefer lit fic, horror, thriller, psychothriller, contemporary drama. Romance is okay. The story doesn't have to center around boxing or any specific sport, but I'd like the protagonist to be an athlete of some kinda combat (?) sport.