Boyka: Undisputed 4 is the fourth film in the Undisputed franchise, and the third to star Scott Adkins as Yuri Boyka, who began as the antagonist in the second film and became the protagonist in the third one, where he earned his freedom after winning the Prison Spetz Competition. After escaping to Budapest, he begins a new life fighting in underground clubs to make a name for himself. His efforts attract the attention of professional fighting scouts, as well as earning him a fight for the European MMA championship.
After he wins, he learns that his opponent has died from the beating and is overcome with regret and concern for the man's family. He then risks his freedom by returning to Russia to seek out the man's wife (Alma) to make amends, learning her husband had taken out a loan with a crime boss named Zourab. Since he died before it had been paid back, Zourab now claims Alma as recompense against her will. Boyka offers to fight for Zourab to wipe Alma's debts clean and redeem his soul.
This film has examples of:
- Aesop Amnesia: The previous film showed that Boyka's loss to Chambers taught him humility. But by the time this film's events occur, he's fallen back into his old ways, which results in him accidentally killing an opponent in the ring.
- Always Someone Better: In Boyka's absence from his former prison, the bigger, meaner and more dangerous Koshmar has replaced him as the undisputed champion. His reputation is such that Zourab pays to have him temporarily released from prison in order to defeat Boyka. It also appears that Zourab has replaced Gaga as the Russian Mob emissary controlling the prison, and likely his other business interests as well.
- Anti-Hero: Boyka is very arrogant and doesn't know how to restrain himself in the ring, which results in him killing an opponent in the ring. However, he does still possess a conscience, which leads to the rest of the events of the movie, as he risks going back to prison just to make things right with his deceased opponent's family.
- Arrogant Kung-Fu Guy:
- Boyka is an arrogant showboater who enjoys brutalizing his opponents. He has to learn how to grow beyond this after accidentally killing Viktor during a fight. Zourab's elite enforcer, Igor, is similarly smug and loves to dish out trash talk.
- Koshmar has shades of this under his blatant psychopathy, considering how poorly he reacts to Boyka getting the edge over him during their fight.
- Artistic License – Martial Arts: Not to the extent of the high-flying stunts seen in the previous film, but Boyka's lavish kicks still aren't exactly presented as practical.
- Ax-Crazy: Koshmar is a psychotic prisoner that beats people to death with his bare hands. He's so deranged that he has a special restrainment suit that prevents him from flying into a rage.
- Badass Boast: Boyka: "Bring me your fucking champion!"
- Bittersweet Ending: Boyka defeats all of Zourab's fighters and kills him, freeing Alma from his control, and she forgives him for her husband's death. However, he loses his chance of a new life in the process and ends up back in prison, where he'll have to start up again. At least, though, he now has his knee fully healed, meaning this time will be easier than the previous.
- Blood Knight:
- Boyka's tendency toward this behavior is what leads to him accidentally killing Viktor during their fight in Budapest.
- Koshmar in a more straightforward fashion is a violent thug who enjoys beating his opponents into a pulp.
- Determinator: Boyka is willing to do anything to make things right with Viktor's family, even if that means going back to prison.
- Happy Ending Override: By the end of the film, Boyka is again in prison, negating his happy ending from 3.
- Jerk with a Heart of Gold: Although Boyka accidentally murdered Alma's husband in the ring due to his Arrogant Kung-Fu Guy Blood Knight tendencies, he still puts his neck on the line for her when he discovers she is indebted to Zourab. He also gives most of his fight winnings to a church in Budapest.
- Losing a Shoe in the Struggle: Alma is dragged right out of her high heels when she is abducted during the film's climax.
- Meaningful Name: "Koshmar" means "Nightmare" in Russian.
- Mighty Glacier: Koshmar is a hulking mountain of a man who can send his opponents sprawling across the mat with just one or two punches. However, he has little to no evasive options, which leaves him vulnerable to Boyka's grapples and kicks.
- No-Sell: Koshmar gets punched a few times and doesn't even flinch. He just gets angrier. It turns out this only applies to body shots, however. The moment Boyka starts applying most of his force into shots to Koshmar's face, he's left stumbling.
- "Shaggy Dog" Story: Boyka is free from jail and is aspiring to a promising MMA career. However, he must run against the clock to clear out his conscience before he can take a big chance. Ultimately, he loses the chance and is sent again to prison.
- Unskilled, but Strong: Koshmar. He's a lot less technically adept than many of the other fighters, but makes up for it by being incredibly strong, durable, and absolutely fucking insane.
- Unstoppable Rage: The way Koshmar fights as he becomes a monstrous beast when he fights and prefers pure brute strength and rage over skill.
- Worthy Opponent: Boyka's manager warns him that Viktor "fights like he needs to win," just like him. During their fight, Viktor actually comes close to winning, forcing Boyka to fight much more viciously in order to defeat him.
- Wrestler in All of Us: Koshmar is especially guilty of this.
