Beth Ditto sprawled on her back and kicked her legs like a turtle in distress. “No! No! No! No! No!” she screamed.

Ms. Ditto, 38, who spent nearly two decades fronting Gossip, the post-punk dance band, has recently reinvented herself as a solo artist and an actress. She now plays Bets, a seemingly demure housewife on Showtime’s “On Becoming a God in Central Florida,” a dark, sunstruck dramedy. With her cat sweatshirts and curled bangs, Bets may appear sweet. “But she’s really not,” Ms. Ditto said. “She’s a fighter.”

And on a cloudy morning in early October, in the concrete basement of a Union Square studio, Ms. Ditto was fighting, too.

“Ready for a kick in the tiddlywink?” she said, aiming a black toenail-polished foot at the gym-short covered crotch of Rachel Piazza, the founder of Feminist Self-Defense.

“Nice,” Ms. Piazza said, approvingly.

Ms. Ditto had arrived half an hour earlier, an enthusiasm vortex, slipping off her gold sneakers as she signed a series of liability waivers. “I’m feeling self-defensive,” she said by way of greeting.

Outspoken and outrageous, Ms. Ditto, who advocates queer visibility and body positivity, wouldn’t seem to need help speaking up or pushing back. But she comes, she said, “from a long line of scrappy women who had a lot of sass and a lot of wit, and could talk back, but didn’t always fight back and also felt powerless.”

She channels them, her mother especially, when she plays Bets, and she wishes they had known how to protect themselves — emotionally, financially, physically. So when her manager, Tara Perkins, suggested this self-defense seminar, she agreed.

“As a Southerner, a survivor, a woman, it’s something that I wanted to do, a punk rock thing,” she said. “Also as a fat person, rolling around on the ground, I think that’s really cool, too.” Waivers signed, Ms. Ditto stripped down to an off-the-shoulder black sweatshirt and black leggings, and pinned up her red-gold hair. In the harsh light of the anteroom, her lipstick glowed like a neon slash and her eye shadow unfurled like bat’s wings beneath her arched brows. She looked like a Kewpie doll gone goth.

She followed Ms. Piazza and Ms. Perkins into the studio, which felt like an athletic bridal suite with its white walls, white columns and white floor mats. “Come on everybody,” Ms. Ditto said. “I’m going to flip you like a house on an HGTV show.”

Ms. Ditto is a great talker — shrewd, lippy, batting words around like Wiffle balls. Acting, she thinks, is just more talking. “It’s really just learning your lines and saying them convincingly,” she said.

Ponytail swinging, Ms. Piazza gathered her students and gave an impromptu pep talk on feminist self-defense. “It shouldn’t be up to us end violence, but we can have more control over our bodies and our lives if we have these tools,” she said. “I want you to feel more empowered and I want to give you more freedom in your life.”

She also promised to teach the women not just physical defense, but also tools for setting boundaries.

“I have boundary problems,” Ms. Ditto said, jokingly. “Crossing them, sometimes.”

Ms. Ditto also admitted she has a hard time saying no to fans. “I feel really bad not giving them my time,” she said. “I don’t want to feel ungrateful.”

“Communicate that,” Ms. Piazza said.

Ms. Piazza urged the women to their feet. She demonstrated a weak stance — feet together, legs straight — and showed them how unstable it was. She poked Ms. Ditto and Ms. Ditto stumbled back. She then modeled a more powerful stance — feet staggered, hip-width apart — and urged the women to try it. Poked, Ms. Ditto held firm.

Eager for offensive techniques, Ms. Ditto began to chant, “Eyes! Knees! Groin! Throat! Eyes! Knees! Groin! Throat!” It was the chorus from a song on “Free to Fight,” the 1995 album by a group of all-women bands associated with riot grrrl, the feminist movement. The album also took the form of a self-defense project.

Ms. Piazza explained that she wouldn’t be teaching many offensive moves like those. Instead she would instruct the women on jujitsu-style moves, including how to break free when an attacker grabs them. “I watch a lot of true crime,” Ms. Ditto said. “I’ve seen this a lot. So many women are kidnapped like that. It’s always on video surveillance.”

With Ms. Ditto’s permission, Ms. Piazza clasped Ms. Ditto’s waist. Then she directed Ms. Ditto to bring her inside arm underneath the attacker’s arm, freeing herself.

She also taught her students to maintain distance from an attacker by practicing the athletic stance they had learned, breaking holds if necessary, and using words (“No!” “This is not O.K.!”) to call out behavior.

But what if an attacker pushed them to the ground?

“One of the great awesome things about jujitsu, is that we’re completely offensive from the ground,” Ms. Piazza said. Rolling onto her back, Ms. Piazza showed them how to wrap their legs around an attacker, throwing him off balance, and how to kick out toward an attacker’s head.

“Can you kill someone doing that,” Ms. Perkins said.

“Blood sport over here” Ms. Ditto said. “Do you want to get away with it? Make it look like an accident?”

Death was unlikely, Ms. Piazza explained, but a kick to the head would definitely hurt. After the women practiced their kicks, Ms. Piazza said they had time to learn just one more move. “Do you want to try a rear naked choke?” she asked.

“Obviously,” Ms. Ditto said.

Ms. Piazza demonstrated how to come behind an attacker and choke him with a left forearm in front of the neck and a right forearm behind. It looked like a dangerous cuddle. They took turns practicing the move on Ms. Piazza, who would tap their arms when she felt pressure.

Ms. Ditto encircled Ms. Piazza, whose cheeks quickly reddened. She tapped, then coughed. “That was perfect,” she told Ms. Ditto.

This time, Ms. Ditto didn’t have a joke or a taunt or a smart comeback. She wanted to learn to protect herself, not to hurt someone else. So she set a new boundary.

“I don’t think I like that,” Ms. Ditto said. “After this, can I pick you up? Can I do the ‘Dirty Dancing’ lift on you?”

“Absolutely,” Ms. Piazza said.