When Ronda Rousey earned a place on the 2008 Beijing Olympic judo team, she decided to use her newfound notoriety to make a statement.

In a JudoForum.com post, Rousey lit into the USA Judo governing body for what she considered its apathy toward Fletcher Thornton, an official who had been accused by several female athletes of plying them with drugs and alcohol and molesting them while they were in their teens.

"USA Judo didn't bat an eyelash at Fletcher Thornton's DOZENS of documented accusations of molesting young girls," Rousey wrote. "One of our 'A' referees even covered his eyes and refused to look at the police reports these girls filed. This is playing with the safety and careers of our athletes. How is this man still allowed to be in the same VENUE of our athletes let alone protected by USA Judo and kept in an extremely influential position?"

National media outlets picked up on the story, including The New York Times. Without admitting guilt, Thornton resigned shortly before the 2008 Games began. Rousey, now the UFC's bantamweight champion and an A-list sports star, later stated she felt an obligation to make others aware of Thornton's alleged impropriety. Being on the Olympic team, she said, allowed her to speak out without fear of being reprimanded.

Sexual abuse by instructors is not a new phenomenon -- no fewer than 10 criminal or civil cases against grappling instructors have been publicized in recent years, many with several recurring elements: The alleged victim was under the influence of a man she believed to have authority over her; the training rooms were often male-dominated; and the hierarchy of the school made speaking out an uncomfortable proposition.

"It's a situation where you have someone in a high position who isn't often questioned," says AnnMaria De Mars, Ph.D., Rousey's mother and a longtime judo practitioner. "People assume if you can stand up for yourself physically, you can also stand up for yourself emotionally, but that isn't always the case. You can have someone good at a sport that isn't that self-confident."

Unlike most sports, jiu-jitsu, judo, and other ground arts have mixed-gender practices. Because men far outnumber women, training with the opposite sex becomes a necessity, and female coaches are scarce. As more young women seek out training for recreational or professional goals, few expect the situation Rousey spoke out against -- that they would someday need protection against their own instructor.

Former judo star AnnMaria De Mars (left) raised her daughter Ronda Rousey around martial arts but was careful to avoid what she believes has been a longtime problem: sexual harassment and assault by instructors. David Dermer/Diamond Images/Getty Images

At 17, Samantha (not her real name) had just moved to the United States and was feeling overwhelmed. She decided to try a local MMA studio, where she was being encouraged by one of the instructors, "John," to keep at it. The two messaged each other on Facebook.

When Samantha had friends over on a day her parents weren't home, she invited John. After the others had left, Samantha says John forced himself on her in her bedroom. When she informed a female staff member at the gym, John was told to leave; Samantha was asked to not tell her parents. According to Samantha, John threatened that if something happened to him, she might not be safe, either.

After struggling at the school for several months, she left and told her parents everything. Her father, she says, wanted to sue the school, but her mother didn't want to pursue the matter.

Samantha's story is an example of how coercion can happen at schools where "rank" matters. A black belt is automatically deferred to in much the same way a psychiatrist or priest is trusted. In fact, MMA students are encouraged not to question authority. When instructors introduce sexual exploitation or assault, many women interviewed for this story said it can be perceived as an extension of that authority.

"I believe a Brazilian jiu-jitsu instructor's influence on a student is stronger than a doctor, psychologist or lawyer," says Rener Gracie, a member of the legendary martial arts family and a head instructor at the Gracie Academy in Torrance, California. "They put students in impossible scenarios where they have no answer and then teach them the solution. It puts them in a position of being a purveyor of absolute truth and effectiveness. And if this instructor has this degree of truthful knowledge, they must have same answers for life."

That deference had led to a number of students being targeted by instructors, with an alarming number of victims who were underage. In January 2012, former UFC lightweight fighter Hermes Franca was convicted of attempted sexual abuse of a minor. Upon his release in April 2014, he was deported to Brazil. (The legal guardian of Franca's victim is currently suing Franca's school and his team manager, Mark Wright, in a civil suit for allegedly allowing situations in which Franca could be alone with her. The family is seeking $905,000 in damages.)

In April 2014, Yakima, Washington, jiu-jitsu instructor Cristiano Oliveira was arrested and held under suspicion on a count of third-degree child rape. (He's been held on a $1 million bond, and his case has not gone to trial.) He was the head instructor; his alleged victim was a student under the age of 18. In 2012, Oliveira allegedly had agreed to offer free lessons three times a week to underprivileged children.

In 2013, New Hampshire instructor Aldo Batista dos Santos was charged with multiple counts of felonious sexual assault against a teenage student. A mistrial was declared in August 2014 when a relative of the alleged victim began screaming at dos Santos' lawyer during cross-examination. Dos Santos was subsequently found guilty in a December jury trial.

"He created an atmosphere where you weren't allowed to question him," says a former male student at dos Santos' academy who asked not to be identified. "When the case broke, he said the student was just trying to sue him for money. But it's a criminal trial."

Deference to an instructor is not the only cause. With most martial arts schools, many parents allow teens to travel with coaches to competitions in neighboring states and away from any other supervision. Livermore, California, judo instructor Ryan Rebmann was convicted of molesting two underage students in 2009 and 2011. One instance was during a road trip.

Another Olympic judoka, Kayla Harrison, made headlines in 2011 when she detailed how she had been subjected to sexual abuse by her coach, Daniel Doyle, as a teenager. Doyle was eventually sentenced to 10 years in prison.

When Rousey was 15, she qualified for the junior world championship in Brazil. De Mars got a phone call from USA Judo asking whether her daughter would be attending.

"Who's going to be on the coaching staff?" De Mars asked.

"That hasn't been decided," the representative said.

De Mars gave a very quick no -- she was not going to send Rousey out of the country with someone she didn't know. "If you took the sport component out of it and asked someone if you could take their 15-year-old daughter on a trip, there's no way," she says. "There is no magic just because it's a martial art."

In another instance, De Mars recalls a camp she and Rousey attended while Rousey was still a teenager. Rousey informed her that a male participant was being cited by other females in the gym as someone who was touching them inappropriately but in a way that could be construed as "accidental." De Mars approached the man and told him he was not welcome.

"I tried to be fair, but what are the odds, out of the 55-odd men in the camp, all the girls are complaining about this one guy?"

In grappling, physical proximity and opportunity often conspire to make vulnerable students available to predators. Although underage females appear to be a primary target, adults are not exempt from abuse -- and it's not always physical.

"Chauvinism is true in more gyms than not," says De Mars, who has visited many of them in a judo career spanning decades. She likens female athletes in combat sports to women who enter the technology fields: She designs games as chief executive officer for 7 Educational, a learning software company. Both areas, she says, are male-dominated and can frown upon women in the form of misogyny and harassment.

"You're often the only woman in the room. And you're told to your face you're not as good, that you don't belong," she says. "It unfairly requires you to have a thick skin."

Rachel Piazza, a New York-area martial artist who earned a master's degree in women's and gender studies, got involved with jiu-jitsu for all of the typical reasons. She wanted to learn self-defense and improve her health. Several years into her training career, Piazza found herself opposite a male student who didn't take her ambitions seriously. Despite Piazza being a purple belt -- an intermediate, hard-earned ranking -- her teammate made inappropriate comments and jokes, once referring to her as a "prostitute" and another time insinuating she was pleasuring herself with a foam roller. She complained, but felt as though other students didn't take it seriously.

"Part of the problem is that men get away with sexist behavior in their everyday lives," she says, "and gyms can serve as spaces where this behavior isn't only tolerated but celebrated."

As MMA continues to provide opportunities and exposure for women -- with this weekend's back-to-back Invicta and UFC 184 cards acting as watershed moments for women as headliners -- more practitioners are taking it upon themselves to provide a safe climate for newcomers.

Texas-based jiu-jitsu purple belt Shama Ko, who organizes the nationwide, female-friendly Girls in Gis training events, had 15 attendees for her first date in 2009. This summer, over 250 women showed up across three states. "I have more requests for events than I can put on," she says.

Ko's work is an attempt to fill in the gap created by the industry itself. There is no governing body overseeing academies. Background checks are left up to the individual owners. Some schools even lack changing rooms for women participants, adding to the sense of isolation. And sexual harassment policies are virtually unheard of. Often, the climate of a gym can only be measured once you become a member. And by that time, women might have already experienced their share of sexist remarks or worse.

"I would look at the energy of an academy," Gracie says. "If it becomes clear newer students are there to serve as grappling dummies for advanced students, it could mushroom into something much more serious. The goal of an experienced grappler is to get others to his or her level. If that's not present, get out. Don't wait until you get injured or assaulted."

Sexual abuse is often preceded by time spent out of the gym, either traveling with instructors or engaging in social media communication with them. (It was alleged Franca would drive his victim to and from his gym.) De Mars recalls an incident when she insisted on staying in a school where she saw only a teenager and the coach present until the student's parents picked her up. It's foolish, she says, to entrust a stranger with a minor simply because he has a black belt.

De Mars was recently asked by a friend what she could do to help her stepdaughter, who suffered from low self-esteem. After hesitating, De Mars expressed sympathy and suggested some counseling. Although a 40-year veteran of judo would seem likely to endorse grappling, she didn't know any instructors in the area and therefore had no idea whether any were reputable -- especially for someone emotionally vulnerable. It wasn't that she didn't endorse grappling; it was that she didn't know whether this young woman could be guaranteed a safe environment.

For that reason, she was sorry to say, "I didn't think martial arts would be the best idea."

Although women remain a minority on the mats, De Mars is optimistic that their continuing presence will alleviate prejudicial or predatory behavior.

Or, as Ko puts it, "Eventually, the hope is that you'll stop seeing gender and just see jiu-jitsu."