Momma's Boy is a mission in the DLC episode The Ballad of Gay Tony. It is give nto Luis by his mother.
Luis finds out that his mother is in debt and an official for the underground Cage Fighter's League forces him to step into the ring. Luis first fights a fat man, then one with brass knuckles, and a large man that used to be his rival, apparently. He is instructed to "take a dive" in the last match. If Luis doesn't take the dive, you have to kill the promoter.