The story Nico tells Scott about why he was unable to fight in the UFC is based on actor's (Bas Rutten) own experiences. Shortly after beginning his career with UFC, while training for his third fight, he blew out his knee, as well as sustained other injuries forcing him to retire.
When Nico is trying to train Scott in his gym prior to his second fight, Nico mimics punching Scott, calling out "Liver shot" at one point. Bas Rutten (Nico) became well known during his fighting career for favoring punches and kicks to the liver of his opponents.
Prior to filming, Bas Rutten met a man at a party who tried to claim that he knew a unique form of "Street Karate" which had a special routine of fight moves that had "saved his life six or seven times" from attackers in the past. Oblivious to the fact that Rutten was a professional martial artist, the man then demonstrated the his routine, which consisted of a string of obviously choreographed and impractical head-butts, knee strikes and stamps. Rutten was so amused by this mans obvious lie that he incorporated the man's alleged "routine" into his Niko's dance class in the film.
Near the beginning of the film, Scott Voss is "teaching" his class, and puts a newspaper over his head. On the paper is a photo of a hockey player with the headline "Season Suspended", suggesting a suspended hockey season. When this film was released in the Fall of 2012, there really was a suspended hockey season due to a player lockout.
In Scott's second MMA bout the opponent he fights is famed MMA trainer Rafael Cordeiro. Cordeiro came into prominence training fighters such as Anderson Silva, Shogun Rua, and Wanderlei Silva from the legendary Chute Box camp in Brazil. He has since moved to Orange County, CA and started his own King's MMA Academy.
Reactions shots for the MGM Grand fight were filmed at the old Everett, Massachusetts High School, which Ellen Pompeo graduated from in 1987 and was also used as a base camp for filming of Boston's Finest (2010).
The trivia item below may give away important plot points.
The last fight of the movie took place at UFC 178. That event didn't feature Carwin vs Dos Santos as featured in the movie. Cain Velasquez was the champion and Carwin had retired. The card was headlined by Johnson vs Cariaso for the flyweight championship, and there wasn't a single heavyweight bought the whole night.