A professional mixed martial arts fighter based in Berlin, Niko Samsonidse, has added a ritual to his tournament prep in recent years: vetting the event to ensure it is not organized by far-right extremists.

Urging other fighters and trainers to do the same, Mr. Samsonidse has become outspoken in his efforts to call out attempts to exploit the growing martial arts scene to advance extremist ideologies.

Mixed martial arts, or MMA, “is getting way more popular in Germany, and mostly they’ve got nothing to do with extremism,” said Mr. Samsonidse, a social worker who wrote his thesis on fighting extremism in combat sports.

“But most of the people, they are not aware what’s happening beside of them,” he added.

Neo-Nazi groups in Germany and across Europe have worked to co-opt martial arts as a training and recruiting tool — hosting high-profile combat sports festivals and offering local opportunities to practice the sport — to try to broaden the groups’ appeal, experts say.

It is part of a larger strategy to make the face of extremism more mainstream. Festivals or tournament organizers market their events in a way that makes them hard to distinguish from normal combat sports tournaments. They then use the events as a gateway to soften up potential recruits to their ideology.

The festivals — which are often declared political events, making them harder to ban and ensuring that any profit will be tax-exempt — typically feature a right-wing extremist speaker or seminar, according to Hans-Jakob Schindler, the Berlin-based senior director of the Counter Extremism Project. And while mixed martial arts tournaments in Europe typically feature fighters from different racial groups, these events allow only white fighters to take part.

“They’re trying to broaden the capture area,” Mr. Schindler said. “You get people to buy the T-shirt, you can get them to come to one of the festivals. And you slowly begin speaking them to them about how the political system is bad. And so you draw them in a bit more subtly than you did in the past.”

In the promotional videos for the largest extreme-right combat tournament, called “Kampf der Nibelungen,” or “Battle of the Nibelungs,” there are no far-right symbols or slogans on display. Focused instead on the boxing ring, the ring girls and the heavily tattooed fighters, the only indication that the event is out of the mainstream is that the participants’ faces have all been blurred.

But the message underpinning the events, said Alexander Ritzmann, a senior adviser at the Counter-Extremism Project, is clear: “that whites are under threat on all kinds of levels.”

Some of the participants have openly cast their efforts to learn martial arts as preparation to fight back against those they see as threatening white European identity, the Frankfurt Roundup newspaper reported, quoting a martial arts fighter who took part in the Battle of the Nibelungs, Germany’s most notorious far-right combat sports tournament.

“In this day and age, it’s so obvious that our people have their backs against the wall, and we all have concerns about our survival,” the unidentified fighter said on a far-right podcast in 2015, adding that the day would come when “we have to put ourselves in a ring with all these multicultural people.”

In Thuringia, an area in the former East Germany, four men between 21 and 25 are facing charges of assaulting law enforcement officers during protests against coronavirus lockdowns.

Federal prosecutors say the men led a far-right martial arts group called Knockout 51 and “attracted young, nationalist-minded men, deliberately indoctrinated them with right-wing extremist ideas and trained them for physical confrontations with police officers, members of the left-wing political scene and other people considered worth fighting.”

The group, prosecutors said, led regular martial arts training sessions at the local office of the National Democratic Party — Germany’s neo-Nazi political party — as well as “ideological training” that included patrolling the neighborhood to scout for political opponents. They sought to kill individuals associated with “the left-wing extremist scene,” according to prosecutors.

In one episode in 2020, according to prosecutors, members of the group kicked a police officer in the stomach at an anti-lockdown protest in Berlin, and months later at a protest in Leipzig, a member threw a bottle at officers, injuring a bystander.

The lead defendant’s lawyer, Steffen Hammer, has sought to have the trial dismissed, asserting that prosecutors forced his client to give information in a separate case that bolstered the current charges against him.

Mr. Hammer, formerly a singer in a far-right rock band, has denied that his client led a neo-Nazi group, arguing that the martial arts group was apolitical and the victim of overzealous prosecution, Der Spiegel reported.

Large-scale martial arts organizations and events have proliferated for years in Germany, chief among them the Battle of the Nibelungs, which attracts hundreds of right-wing extremists from around Europe and the United States. The name is a reference to the 13th-century German heroic epic poem called, “Song of the Nibelungs,” a text that was often venerated and referenced in Nazi propaganda during World War II.

The Battle of the Nibelungs, which moved to Hungary after it was banned from the German city of Ostritz in 2019, is organized “by young Germans who are united by the dedication and enthusiasm for ‘their’ sport and who do not want to be subject to the yoke of the prevailing mainstream,” according to the group’s YouTube page.

In an effort to crack down on such groups, German law enforcement has conducted extensive raids on members of the martial arts clubs and, in some cases, has banned the clubs or events themselves. The four men associated with the group Knockout 51 currently facing charges in Thuringia were arrested after 800 police officers raided the homes of 50 suspected right-wing extremists in April.

MMA groups with a far-right bent are spreading across Europe and the United States. Mr. Ritzmann said 23 active far-right martial arts clubs already operated in France alone.

“This does not mean that they’ll all turn into neo-Nazis,” he said. “Many, I guess, might drop off at some point. But really mainstreaming this combat sports approach could be a game changer.”

In Germany, leaders in the martial arts community have sought to push back on their own.

Daniel Koehler, the director of the German Institute of Radicalization and De-radicalization Studies, a nonprofit group, founded a network of martial arts schools against violent extremism that seeks to monitor for signs of radicalization in their studios and keep their students away from extremist environments.

Several years ago, Mr. Koehler said, he remembered that studios in his network “regularly” had discussions about members of their gyms whom they later learned had far-right tattoos or clothing.

“They would have to decide, is this someone who’s been with us for a long time; we need to initiate an intervention,” he said. “Or, is this someone who just recently showed up, so we can move the person out?”

His network tries to ensure that participating gyms would “not by coincidence take part in a tournament that, for example, the far right would benefit from,” Mr. Koehler said.

Mr. Samsonidse, the professional mixed martial arts fighter, said that programs giving young adults the opportunity to practice combat sports and impart positive values could be an important way to prevent the rise of far-right extremism in his sport.

“There’s a big potential in martial arts itself, to share good values — respect, controlling your emotions — which could be really useful in work with juveniles,” he said. “But it can also be misused.”