The phrase "undisputed champ" means that someone is recognized as the absolute best or the winner, without any doubts or disagreements. Full definition
When things get ugly, a fellow convict named Ripstein (Falk, Corky Romano) sees an opportunity to earn cash by promoting the fight of undisputed champs in a prison bout, with Hutchen coming in at 40 to 1 odds. (qwipster.net)