Mason Fowler will be defending his belt for the third time against Bellator heavyweight champion and former light heavyweight champion Ryan Bader. A former NCAA wrestling standout, Bader presents a different challenge than previous defenses. Also on the card, Craig Jones will face Vinny Magalhaes, who are both decorated Brazilian Jiu-Jitsu practitioners, along with former judo Olympic gold medalist Satoshi Ishii. Fowler won all of his previous defenses in the overtime ruleset.

Submission Underground 23 takes place on May 23, 2021 in Portland, Oregon.