Sam Mendoza’s oldest son started doing competitive mixed martial arts when he was about 10. His youngest son began when he was six.

During competitions, Korey and Sammy (now 14 and 11, respectively) use moves from multiple disciplines—including wrestling, kickboxing, and jujitsu—against their opponents. Kids Sammy’s age or younger are paired against both boys and girls; but since Korey is over 12, he only spars with boys.

Kids’ mixed martial arts (MMA) is modeled after the adult version popularized by the Ultimate Fighting Championship—a sport so controversial New York didn’t legalize it until last year. (It is now legal in all 50 states.)

Although youth MMA is less well known and less brutal than its grown-up inspiration, it too has faced its share of criticism. In a 2008 article, MMA commentator Sam Caplan wrote that “It should be illegal for anyone under the [age of] 18 to compete in a mixed martial arts fight.” And Mendoza, who organizes youth MMA matches with the United States Fight League in San Bernardino, California, is certainly aware of this sentiment.

“A lot of people think I’m crazy,” he says. “They think I’m a bad parent.”

But youth MMA as practiced by the U.S. Fight League isn’t the same as what you’d see at an adult UFC match. Kids aren’t allowed to strike their opponent’s head or knock anyone out. For further safety, all contestants must be checked by a physician before and after fighting. Fighters wear headgear, and promoters must also have an ambulance stationed outside during fights. So far, the league hasn’t recorded any concussions in 222 paired fights between October 2014 and May 2016.

John Rodriguez and Adam Brooks, both M.D.s and orthopedic sports medicine fellows, have been using the league’s records to study sports injuries in youth MMA. (Rodriguez’s fellowship is at the Andrews Research & Education Foundation, and Brooks’ is at the University of California, Los Angeles.)

Rodriguez says that because most sports don’t have a physician examine kids before and after activity, “the chance of missing a concussion, I think, is a lot higher in almost every other youth sport” than it is for the MMA practiced by the U.S. Fight League.

That said, the league’s data doesn’t include injuries that might be sustained during practice. And as Brooks notes, “you spend a lot more time training than you do in the actual fight.” Ultimately, Rodriguez and Brooks say that they don’t have enough data yet to say how safe youth MMA is compared to other popular sports like soccer or football.

Since 2014, the U.S. Fight League has registered about 240 fighters ages eight to 17 in California and Missouri, the only two states where youth MMA is regulated. And U.S. Fight League founder Jon Frank hopes that youth MMA becomes regulated in other states. He says that it can boost kids’ discipline and self-esteem, but emphasizes one benefit above all others.

“At the end of the day, it’s a form of self-defense,” says Frank. “And if you’re going to take the most effective form of self-defense, there’s nothing that comes close to mixed martial arts.”

Frank adds that a lot of parents get their kids involved with MMA because they are worried about bullying. And when GQ correspondent Drew Magary reported on kids MMA near Orlando, Florida, he also picked up on this, writing: “Bullying is the number one reason kids wind up here.”

The fact that MMA is a form of self-defense doesn’t mean that Frank wants kids to take their fighting skills outside of the ring. Yet as more kids begin to practice the sport—both in states where it’s regulated and states like Florida, where it isn’t—conversations not just about its safety, but also its legitimacy as a sport for kids, are poised to come out of the cage and into the mainstream.