Mark Kerr's former coach and friend Bas Rutten plays himself, as does Stephen "The Fight Professor" Quadros, a former (English) Combat Commentator for PRIDE.
The Rock is only three years younger than the real life Mark Kerr, while the film covers his time competing in MMA which happened when he was in his 30s.
Each day on set required makeup that took three to four hours to complete and 21 prosthetics, courtesy of Academy Award winner Kazu Hiro, to make Dwayne Johnson look like Mark Kerr. Johnson worked with a voice coach to turn his speech into that of Kerr's, a soft, tender voice. The result has been a performance that critics have lauded as one of Johnson's best, who looks almost unrecognizable on the big screen. "I've never worked harder, and we like hard work, it's what we all like to do," Johnson told ESPN during the roundtable. "But man, I had never worked harder for a role."
In the 2000 PRIDE Grand Prix fight scene between Mark Kerr and Kazuyuki Fujita, Dwayne insisted on being hit for real, a request which actor Yoko Hamamura initially refused. He was talked into it by Benny Safdie, and ended up giving Dwayne a concussion, to achieve that legitimately dazed look on Mark in the movie.
To help deal with the darker moments on set between Emily Blunt and Dwayne Johnson's characters, tequila was on set for the actors, according to Emily.