The Circuit (2002) on Netflix

Dirk Longstreet is a University professor. But ten years ago, Dirk Longstreet was actually Dirk Lincoln, the Eastern Seaboard Champion of an illegal underground fighting society, known to its members as 'The Circuit'. Dirk is happy with his new name and profession, but when his brother (Jeremy) enrolls in the fighting society to make money. Longstreet has to make a choice - let Jeremy learn from his own mistakes, or step back into the vicious underworld he walked away from. Dirk infiltrates his way back into the underground pit fights to face The Circuit's new champion, Kwan (the tiger Twins), and the new owner of The Circuit, Vixton.