Law enforcement sources tell us ... the former IBF junior middleweight champion is telling investigators ... he was hanging out in Hollywood early Friday morning when he struck up a conversation with a guy he just met.
Former pro boxing champ Kassim Ouma was arrested for battery in L.A. on Friday -- after knocking out a man who was allegedly making gay advances toward him ... TMZ Sports has learned.
Ouma says the two went back to the other man's home for a drink ... where the guy allegedly made a pass at the boxer.
We're told ... Ouma claims he politely declined multiple advances ... but says when he got up to leave, the guy made one final move -- and Ouma shoved him away.
The altercation then escalated ... with Ouma allegedly knocking the guy out cold.
Cops were called to the scene -- where the victim was treated and transported to a nearby hospital.
Ouma was ultimately arrested for felony battery causing great bodily harm.
We tried to contact Ouma for comment -- but he's still behind bars.