Photo: Carlos Avila Gonzalez, The Chronicle Photo: Lance Iversen, The Chronicle Photo: Gabrielle Lurie, The Chronicle

Golden State Warriors All-Stars Stephen Curry and Klay Thompson, it is often noted, were winners of the genetic lottery, sons of NBA stars.

But it’s possible that an even more vital element is overlooked when it comes to measuring what makes the Splash Brothers great: the Splash Mothers.

Sonya Curry and Julie Thompson drove their kids to practices, exerted discipline and instilled values, sure. But it goes deeper. The two moms were athletes. Really, really good athletes.

Read and learn, Steph and Klay.

You both know that your mothers were standout college volleyball players, blessed with athleticism and grit. But because your moms did not decorate the family homes with their trophies and photos, and they didn’t (and still don’t) talk much about the glory days, it’s possible you two aren’t fully aware of just how much of what you do on the court, physically and emotionally, is a hand-me-down from mom.

Have you guys ever talked to your mom’s old coach?

“Julie, athletically, is as good as anybody I’ve ever coached,” said Steve Pickering, one of Klay’s mom’s college volleyball coaches. His coaching career spans four decades.

As for Steph’s mom, after Sonya Adams’ magical sets powered Virginia Tech to an upset over powerhouse Cincinnati, Cincy’s coach approached Sonya’s coach to propose a trade: Cincy’s team bus and van in exchange for Virginia Tech’s shrimpy setter.

The Splash Mothers could be twin sisters.

•Both grew up in athletic families and began to play sports when they began to walk. In high school, both were star sprinters and volleyball players. Sonya also excelled in basketball.

•Both were undersize. Julie was a 5-9 outside hitter, a position often reserved for women over 6 feet. Sonya was 5-5, also an excellent leaper, though, unlike Klay’s mom, she could not dunk a tennis ball. (“No, my mom couldn’t do that,” Steph deadpanned. “Neither can I.”)

•Both were quiet, serious, determined, self-motivated team leaders.

•Both met their future husbands in a gym — a classic case of love at first sight. Both leave most of the talking to their husbands — Dell Curry is a color commentator for the Charlotte Hornets, Mychal Thompson is a radio color announcer for the Lakers.

•Each raised three outstanding athletes. Klay has two brothers: Trayce, an outfielder for the Dodgers, and Mychel, who plays for the Warriors’ G-League team. Steph’s younger brother, Seth (currently injured), plays for the Dallas Mavericks, and sister, Sydel, was a volleyball star at Elon University until being forced to retire before her senior season due to concussions.

•Both refused to push their kids into any sport. But once the kids committed, these moms demanded full effort.

“I was short, fast and mean,” Sonya Curry says, summing up her athletic attributes.

Sonya Adams was an eighth-grader in Radford, Va., when the local high school volleyball coach, John Pierce, promoted her to the varsity team.

When Sonya was a senior, Radford High won the state AA championship and she was Virginia defensive player of the year. In basketball, as a defensive specialist, she led the Radford girls to two state titles. In track, Sonya competed at the state level in the 400-meter hurdles and sprint relays.

“Just an astonishingly good kid,” recalls Pierce. “Really delightful young girl, just fun to be around. She was small then, and she stayed small, but she already had a great work ethic, great parental support from her mom, Candy, who did not play around. Candy’s kids toed the line.”

As high school came to an end, Sonya had multiple college offers. Some wanted her for volleyball and basketball. Pierce, of course, hoped his prodigy would choose Virginia Tech, because he coached the women’s volleyball team there, also. But he encouraged her to shop around. Sonya was driving home from a recruiting visit to James Madison when she fell asleep and crunched her car into a guardrail.

Sonya now says, “I was just like, ‘You know what? I’m going to stay close to home.’ The car was a little tore up, and I was like, ‘That’s a sign. Don’t go to James Madison.’”

If Sonya needed another reason to choose Virginia Tech, she got it during her official recruiting visit when she watched the men’s basketball practice and homed in on the team’s star, Dell Curry. Dell noticed back. As one of Sonya’s classmates told The Chronicle’s Ann Killion, “Sonya was not an ugly girl.”

Photo: Courtesy USF

Sonya made all Metro Conference as a junior, then hung up her sneakers to follow that Dell Curry fellow to Utah for the start of his NBA career.

Julie Leslie grew up in Ridgefield, Wash., about 20 minutes north of Portland, Ore., with two sports-loving brothers. Her first love was gymnastics, but she could run like the wind, and loved all sports. She discovered volleyball as a high school sophomore and, a bit sadly, quit gymnastics.

During Julie’s junior and senior seasons, the Ridgefield High girls volleyball team finished second in the state in 1980 and ’81. In track, Julie won the state Class-A long jump title at 18 feet, 6½ inches.

She had scholarship offers from Oregon State and University of the Pacific, but chose smaller University of Portland, a National Association of Intercollegiate Athletics school, because, she said back then, “At (OSU and Pacific), volleyball is No. 1, and I wanted my schooling to be No. 1.”

Julie was a starter from day one for rookie coach Steve Pickering. The team won the conference championships two years in a row, a big turnaround for the program, “And Julie was a big part of that,” Pickering says.

One day, Julie went to the university gym to play some volleyball and happened to see a pickup basketball game. One of the players was Mychal Thompson, prepping for his second season with the Portland Trail Blazers.

“I saw her out of the corner of my eye,” says Mychal. “I forgot about the game.”

After Julie’s second season, Pickering took a job at the University of San Francisco, and Julie decided to make the move, too. She red-shirted her first season there, but during the next season, in a match against Pepperdine, she blew out a knee ligament.

After recovering, she played her senior season under a new coach, Laurie Corbelli.

“I remember when I first met her,” says Corbelli, who recently retired as coach at Texas A&M. “She had this gorgeous smile, she just stood out because of how strikingly beautiful she was, and how sweet. Almost too sweet for words. I thought, ‘How does this girl get after it on a volleyball court?’

“But what a fluid and graceful athlete!”

How good was she? Mychal is not an impartial witness, but he insists, “She was good enough to play on Team USA. She could really play. She could dunk a tennis ball, how about that?”

“Mychal is ridiculous,” Julie says in a separate interview. “He brags too much.”

Nobody had to tell young Klay Thompson that his mom was an athlete. Every month or so, mom would challenge Klay to a race on the family driveway.

“I couldn’t beat her until I was 14 years old,” Klay says, with a combination of pride and shame.

When Klay finally did beat mom, “That was a great moment for me. I remember it like yesterday. She wouldn’t give it to me, I had to earn it, and it took me 14 long years.”

Says Mychal, “Julie would not let Klay win. She wasn’t sympathetic, she wanted to teach the boys that life ain’t fair, sometimes you gonna get beat.”

Julie says she had forgotten about those driveway races, “And I can’t believe he remembered. See? People don’t think Klay is paying attention. He pays attention. He’s so funny.”

That quote demonstrates one of Julie’s little tricks, turning the conversation away from herself. When I asked Klay if his mom would talk to me about her athletic career, he said instantly, “Not a chance!”

Sure enough, Julie didn’t return calls until her husband nagged her into it, telling her she was being rude.

“I just don’t want to talk about stuff I did 30 years ago,” she says. “It’s boring.”

For her, sports was never about the glory. When she was dominating track meets as a kid, Julie never bothered to pick up her ribbons and medals. Her mom would scramble to do that, unbeknownst to Julie.

Her kids wouldn’t know she was a star, if not for Mychal.

Julie doesn’t recall coaching her kids, but Mychal says, “She would show them how to run. She’d talk to them all the time about the proper way to run, about stretching, yoga, doing different exercises, like Pilates. She still does this, still preaches to them today.”

A couple of years ago, Klay seemed to be pressing. Julie suggested that before the game, instead of listening to music or playing video games, he read a newspaper. He does that to this day.

You won’t catch Julie bragging about how she motivated Klay. But defend him?

“I used to get really tired of hearing that Klay’s not athletic,” Julie says. “You know what? This kid is a gamer, and he has been since he was really young. ... And I know Klay, he hates to lose.”

Wonder where he gets that?

Steph Curry knows his mom was an athlete.

“She was ferocious,” Steph says. “People say I get my feistiness, my aggressiveness from her.”

Sonya left most of the technical coaching of the kids to Dell, but she had input on the mental and emotional side of athletics. Dell says this was important, since he spent so much time on the road over 16 NBA seasons.

Says Dell, “The fact that she knew what the kids were going through competitively, and how to react to different situations, was definitely big.”

But don’t think that Sonya was the quiet psychologist.

“Every AAU game I played,” Steph says with a smile, “she would sit in the front row and scream at the top of her lungs, what I’ll call suggestions. She was never shy about giving her input, and she knows what she’s talking about.”

Mom and son would talk on the drive home from games.

“It wasn’t so much X’s and O’s,” Steph says, “it was more about mentality, being aggressive, being confident, taking pride in what you do. It wasn’t like, ‘Oh, when you come off the pick-and-roll, make sure you look for that split.’ She knew when I didn’t play my best game and was out there lackadaisical, or not focused, or timid or whatever. She could speak to those points.”

Did Steph welcome that coaching?

“She was at pretty much every game,” he says, “so, one, you had no choice, because she was going to tell you. And two, like I said, she knew what she was talking about.”

Sonya says Steph was receptive to her input.

“My other two children absolutely did not” listen to her coaching, Sonya says. “But Steph, he wanted to know, he wants to learn. He paid more attention to my loudness than the other two did.”

The three Curry kids were small for their ages and sports, and Sonya reminded them they had to overcome that disadvantage with hustle.

“The competitive side,” Sonya says, “is I just want my kids to beat the crap out of people when they’re out there. Let them know you’re there, let them know you’re there for a reason.”

Along with the toughness, Sonya imparted what Warriors head coach Steve Kerr would call a sense of joy. If you’ve seen Steph’s three-point-celebration shimmy, you can appreciate this: He says his mom hates to lose, then he quickly corrects himself.

“I wouldn’t say she hates to lose,” Steph says. “She loves winning. There’s a difference.”

Scott Ostler is a San Francisco Chronicle columnist. Email: sostler@sfchronicle.com

Twitter: @scottostler