LSU superstar Leonard Fournette is apologizing for the 1-on-1 incident with his teammate Garrett Brumfield -- but insists the incident was NOT a real fight.
"I would like to apologize to everyone, but we were not fighting, just slap boxing," Fournette tweeted.
"But again I would like to apologize to everyone again."
TMZ Sports broke the story ... Fournette traded shots with Brumfield near Tiger Stadium earlier this week. LSU officials say they believe Leonard's story ... claiming it was just simple horseplay.