If you’re asking “what famous boxers have.moved.to.other combat sports,” notable examples include James Toney, Ray Mercer, Art Jimmerson, Holly Holm, and Claressa Shields, who crossed into mixed martial arts (MMA). Their results ranged from brief crossover appearances to major success, showing that boxing skill alone does not guarantee an easy transition.
Here’s what each fighter tried, how the new rules changed the challenge, and what separates a one-off fight from a genuine career switch. You’ll also find a comparison table to help make sense of the most prominent moves.
What famous boxers have.moved.to.other combat sports?
The clearest examples are boxers who moved into MMA. James Toney and Art Jimmerson tested themselves in early UFC events, while Ray Mercer scored a quick win in an MMA bout. Holly Holm became a major MMA champion, and Claressa Shields pursued MMA while continuing her boxing career.
These fighters did not all make the same kind of move. Some entered the cage for a single high-profile fight; others trained for a new sport and competed repeatedly. That difference matters: a crossover bout makes a boxer a participant in another sport, but it does not necessarily mean the boxer built a second career there.
Famous boxers who competed in MMA
James Toney: boxing champion to UFC challenger
James “Lights Out” Toney was a decorated professional boxer before facing Randy Couture at UFC 118 in 2010. Toney’s experience in the ring gave him sharp punches, but the bout took place under MMA rules, where fighters can grapple, take opponents down, and use submissions.
Couture took Toney to the ground and submitted him in the first round. The match is a clear example of why a boxer’s strength does not automatically transfer to MMA: the opponent can change the range and turn a striking exchange into a grappling contest. Toney’s UFC appearance was a notable crossover, not a sustained MMA run.
Ray Mercer: an Olympic boxer’s MMA knockout
Ray Mercer, an Olympic gold medalist and former heavyweight boxing champion, also tried MMA. In 2009, he fought former UFC heavyweight champion Tim Sylvia under MMA rules at an Adrenaline MMA event. Mercer knocked Sylvia out in the opening seconds.
The result was striking, but it should be read in context. One fast finish does not show that boxing skills cover every part of MMA, just as Toney’s loss does not prove that a boxer cannot succeed in the sport. It shows how much a single matchup can shape the story of a crossover.
Art Jimmerson: an early UFC experiment
Art Jimmerson entered the first UFC event in 1993 as a professional boxer. He wore a boxing glove on one hand and faced Brazilian jiu-jitsu fighter Royce Gracie. Gracie took him down and forced a submission in the first round.
Jimmerson’s appearance became an early illustration of the sport’s central challenge for boxers: MMA opponents are not limited to punches. The fight also took place during the UFC’s early, less standardized era, so it is best understood as a historic crossover rather than a direct measure of how a modern boxer might perform.
Holly Holm: from boxing titles to an MMA championship
Holly Holm followed a different path. After earning major titles in professional boxing, she transitioned to MMA and developed skills beyond her hands, including kicking, wrestling defense, and ground training. In 2015, she defeated Ronda Rousey to win the UFC women’s bantamweight championship.
Holm is the standout example of a boxer who made a lasting move into MMA and reached the top. Her success was not simply a matter of bringing boxing into the cage. She had to adapt her stance, manage kicks and takedowns, and learn how to fight across several ranges.
Claressa Shields: competing in boxing and MMA
Claressa Shields, a two-time Olympic gold medalist and world champion boxer, made her professional MMA debut in 2021. She defeated Brittney Elkin by second-round TKO in a Professional Fighters League bout. Shields later fought Kelsey DeSantis at the PFL-versus-Bellator event in 2024, winning by split decision.
Shields illustrates a crossover that can happen alongside an active boxing career. But MMA is a distinct discipline, not a boxing match with extra techniques added on. A boxer learning it must build grappling skills and practice defending takedowns as well as striking.
How the transitions compare
| Boxer | Other sport | What happened | Best takeaway |
|---|---|---|---|
| James Toney | MMA | Lost to Randy Couture by first-round submission at UFC 118. | A striking background alone leaves major gaps on the ground. |
| Ray Mercer | MMA | Knocked out Tim Sylvia in the opening seconds of their 2009 bout. | A single result can reflect the matchup as much as the transition. |
| Art Jimmerson | MMA | Lost to Royce Gracie by first-round submission at UFC 1. | Grappling was a new and decisive challenge for a boxer. |
| Holly Holm | MMA | Moved into the sport and won the UFC bantamweight title. | Long-term success required broad skills, not just punching. |
| Claressa Shields | MMA | Started an MMA career while also competing in boxing. | A crossover can be a second active career, not a permanent switch. |
Why boxing skills do—and don’t—transfer
Boxing gives an athlete valuable tools: timing, footwork, distance control, and the ability to deliver punches under pressure. Those strengths can be especially useful in MMA, where accurate hands can change a fight quickly.
But boxing rules remove threats that are legal in MMA. A boxer does not have to defend kicks, clinch takedowns, or submissions during a boxing match. In MMA, a familiar stance or a habit of focusing only on punches can leave openings for an opponent to exploit.
- Range changes: Kicks and longer clinches alter the distance a boxer is used to controlling.
- Takedowns: A fighter may need to defend attempts to bring the bout to the floor.
- Ground fighting: Once down, a boxer needs to know how to escape, defend strikes, and avoid submissions.
- Different pacing: Grappling exchanges can use energy differently from rounds spent boxing at range.
That is why Holm’s path is different from a short crossover appearance. A serious move involves learning skills that protect the boxer’s strengths, rather than expecting those strengths to solve every situation.
One-off crossover or a real career move?
Headlines often group every boxer who enters another combat sport into the same category. That can blur important differences. Toney’s UFC bout, for example, was a high-profile test; Holm’s MMA championship came after a broader transition and repeated competition.
Use these questions to judge how substantial a move was:
- Did the boxer train for the new rules? A camp focused on takedown defense and grappling suggests more preparation than a boxing-only approach.
- Was it one appearance or a series of bouts? Repeated competition gives a better sense of whether the athlete is building a career in the other sport.
- Did the athlete develop beyond their original specialty? A boxer entering MMA needs more than strong hands to handle the full ruleset.
- Were the bouts contested under the new sport’s rules? A boxing exhibition against an MMA fighter is still boxing if the contest uses boxing rules.
This last point clears up a common misconception. A famous boxer appearing in a crossover event does not always mean that boxer moved to MMA or kickboxing. Check the rules and the athlete’s actual competition history before describing it as a full switch.
What aspiring crossover fighters should learn
For a boxer considering MMA, the practical lesson is to build the new skills before booking a fight. Start with qualified coaching in wrestling and Brazilian jiu-jitsu, then add MMA-specific training that combines striking with takedown and submission defense. Boxing experience can help, but it cannot replace preparation for unfamiliar situations.
It is also sensible to treat the transition as a gradual process. A fighter should gain experience in controlled training and appropriate competition before facing a high-level opponent. The goal is not to abandon boxing strengths; it is to make those strengths usable under a different ruleset.
For fans, the most useful way to compare these athletes is to separate crossover attempts from successful long-term transitions. Mercer’s quick win, Toney’s submission loss, and Holm’s title run are all memorable, but they tell different stories about the demands of a new sport.
The most famous boxers to cross into other combat sports include Toney, Mercer, Jimmerson, Holm, and Shields. Their careers show that a boxer can bring valuable striking skills to MMA, but sustained success depends on learning the rest of the ruleset.
If you’re comparing a particular fighter’s move, first check whether the bout used MMA rules and whether the athlete competed more than once. That simple distinction helps answer “what famous boxers have.moved.to.other combat sports” without confusing a one-off appearance with a genuine career change.