His stepdad beat him and his mom for years. Now he's a domestic violence expert worldwide.

Ten years of beatings and abuse stopped the day the 14-year-old boy heard his stepdad knock out his mom with one punch.

"There was a loud crack like a gunshot," Mark Wynn said. "She was on the kitchen floor covered in blood. He stepped over her and got a beer out of the refrigerator."

The boy grabbed a rag and wiped blood from his mom's face as she started to regain consciousness. She slowly pulled herself up off the floor, grabbed a baseball bat, went outside and hit her husband in the back of the head, knocking him out.

Wynn was dragging his stepdad off the boy's bicycle when the police got there. Officers took the boy and the two wounded adults to the police station in their Dallas suburb. Wynn's stepdad was locked up on only one charge, public intoxication.

Wynn and his mom got a ride home, where the two packed some belongings, jumped in their Chevy Impala and drove all night to their hometown of Columbia, Tennessee. They never saw their abuser again.

Wynn left behind a home where his stepdad beat him with a belt and his fists and the back of his hand, chased him with a hammer, beat his mom into two miscarriages and put her in the hospital too many times to count, he said.

Wynn doesn't recall much of what he was feeling at that time.

"There was not a lot of reflection; there was only staying alive. That was pretty much all I could focus on," he said, quietly.

"Fear for my siblings and mother — that added another layer of trauma."

Wynn, 68, a nationally renowned domestic violence expert, used that trauma to help fuel him to train hundreds of police departments worldwide and to help start one of the country's largest police domestic violence units in Nashville.

Wynn also will be the subject of a 38-minute indie-film documentary, "This is Where I Learned Not to Sleep," which premieres online for $10 a showing on Kinema.com on Sunday. (Some of the proceeds will go to the Mary Parrish Center, which provides housing and other services to domestic violence survivors.)

The documentary also will be screened nationwide by law enforcement and domestic violence services agencies.

'I saw my mother's face on these victims'

The movie tells the backstory of a man who has been a key part of shifting the nation's thinking toward the idea that violence against family members is violence — and should be punished and treated as such.

"If you're dead, you're dead," Wynn said.

Since his early days on Nashville's police force 44 years ago, Wynn also has quietly and persistently pushed the city's law enforcement into thinking that domestic violence and homicide, with early intervention, are preventable.

That started when he was a rookie, and he and his training officer answered a 911 domestic violence call. A woman met them on the front porch and told them everything was fine, and that they could leave.

The training officer said OK, but Wynn pushed back and asked if he could stay and talk to the woman.

"I mean, it just hit home," Wynn said. "Every homicide I worked in the '80s and '90s, I saw my mother’s face on these victims as we put them in body bags."

In 1994, Wynn started a domestic violence unit. By then, he regularly trained officers in other departments around the country. He eventually trained police in China and Russia and testified about domestic violence in front of Congress, twice.

Wynn's on a mission he feels deep in his soul, one so important to him that he's still consulting law enforcement 23 years after retiring.

It's so important to him that, if given the choice, he'd relive his childhood trauma exactly how it played out.

"I paid a price to learn this lesson and to teach this lesson," Wynn said.

"Look, nobody wants to be a victim, nobody wants to be abused, physically or emotionally. But if I hadn’t been abused, I don’t think I would’ve done the things I’ve done to keep other people from being abused. So it's a small price to pay."

Wynn said he has been sharing more and more about his childhood trauma in his training sessions. And an interesting thing started happening — men privately revealed to him afterward that they were survivors, too.

Then, a year ago, a male police lieutenant stood up in the middle of a crowded documentary screening and shared with the room that he was a domestic violence survivor.

"That was the moment I realized, OK, I don’t mind sharing about my abuse again if it makes another man stand up and say, 'We need to do more,'" Wynn said.

That kind of sharing, he believes, could start a movement that might raise significant awareness of domestic violence and spur a massive pressure to eradicate it.

"If women could stop domestic violence, it would’ve stopped years ago," Wynn said.

"It’s gotta be men. It doesn’t work any other way."

Reach Brad Schmitt at brad@tennessean.com or at 615-259-8384.

This article originally appeared on Nashville Tennessean: Abuse survivor dedicates his life to battling domestic violence