The final showdown between Scott Adkins and Marko Zaror in Undisputed 3: Redemption is the best fight of the series. The Undisputed franchise didn't start off with a big bang with its first entry in 2002, but the straight-to-video sequel Undisputed 2: Last Man Standing defied the odds, switching the series from boxing to MMA and becoming a modern action classic overnight. The sequel also transitioned Adkins' Yuri Boyka from antagonist to anti-hero, pitting him against Zaror's Dolor in a prison tournament with the victor to be granted his freedom - and the stakes of the tournament and Boyka's own personal challenges to overcome are what make Undisputed 3's finale so phenomenal.
Right off the bat, the fighters are extremely incentivized to defeat each other, but things aren't what they seem for the martial arts competition. Boyka and his fellow competitors are forced to perform backbreaking labor while only being granted limited time to train. This is by design since the prison officials, in conjunction with betting mobsters gunning for a big payday, are trying to rig the competition for Dolor. With the villain exempted from the daily labor, able to train freely, and given a steady supply of performance-enhancing drugs, Dolor seems to have his victory laid out right in front of him.
All of that would make Boyka's final duel in the ring a challenge that he'd never faced before, but he's also dealing with the handicap of his bad knee from Undisputed 2. After having his knee shattered by George "Iceman" Chambers (Michael Jai White, also known for another MMA series, Never Back Down), Boyka faces an uphill battle getting back into the ring, and even once he does, a misstep or a well-timed takedown by an opponent causes him to experience surges of momentary pain in his knee. Dolor knows this when they come face-to-face, the two going back and forth in an incredible exchange of kicks and grappling techniques, with Dolor painfully exploiting Boyka's biggest weakness the moment he gets the opportunity.
Boyka's also fighting what he thinks is going to be his last fight, after helping fellow competitor Turbo (Mykel Shannon Jenkins) escape when they learn that losing fighters are being executed. In his mind, Boyka isn't just proving himself worthy of the title of the Most Complete Fighter in the World, but also thwarting a dishonorable tournament. As the most indomitable Scott Adkins character, Yuri Boyka eventually adapts his approach to work around his bad knee and defeats Dolor, only to be rescued by Turbo and Russian mobster Gaga (Mark Ivanir), winning his freedom and his cut of Gaga's earnings from the fight, the crime boss having secretly bet on Boyka.
Adkins himself even regards the final fight of Undisputed 3 as his personal best, and he and Zaror faced numerous challenges during the making of it, from time constraints, taking hits from each other, rehearsing the fight together nightly, and a surprisingly hot floor in the ring itself, all discussed at length by the two on Adkins' YouTube series The Art of Action. That the fight turned out as incredible as it did is testimony to Adkins and Zaror's drive and commitment as performers as much as it is their undeniable skill as martial artists, which is sure to be the case with their respective roles in John Wick: Chapter 4, too. With its storytelling, character fulfillment, and fantastic Larnell Stovall-orchestrated action, Undisputed 3's final fight is the greatest of the series.