She should know. She is both.

“It’s a lot like hockey — fast action, quick on your feet to make a decision, use good judgment, always move your feet, and keep your head on a swivel,” said O’Sullivan.

O’Sullivan, who grew up in the Neponset neighborhood of Dorchester, has 10 siblings, almost all of whom played hockey. She was smack dab in the middle at No. 6. She was on skates at age 3 and playing organized hockey at 5.

“I had five older brothers,’’ she said. “Not that they beat me up, but they definitely challenged me. I had to fight for everything I got.”

When she wanted to play in the old Neponset Youth Hockey League, her father gave the OK.

“He went to register me one day and they said, ‘Oh, girls can’t do this,’ so he took me home, he cut my hair, we went back down, and he signed me up as ‘Steven,’ ” said O’Sullivan.

And long before she went to the Boston Police firing range, she was called a sniper, like her hero, former Bruins star Ray Bourque.

“Yeah, I worked at it very hard,’’ she said. “I’d be down shooting 100 pucks every single day over at Castle Island. I used to come down the left wing and blast it opposite far side of the net. That was my spot.”

She captained the junior varsity of the powerhouse Matignon team in the late 1980s, playing left wing and center.

“She was the only young lady in the program, and I was there 40 years,” said legendary Matignon coach Marty Pierce. “She just treats everybody with dignity and respect and she definitely is a great player.”

Those skills help her as a police officer and co-director of the O’Sullivan Hockey Academy along with her brother Chris, a former NHL defenseman and Boston Police officer.

Classy college career

Growing up wasn’t easy.

O’Sullivan’s father, John, who worked long hours at Boston Edison to make ends meet, died of lymphoma a week before her high school graduation in 1990. Her mother, Ann, died of brain cancer two years later. Even as she battled her illness, Ann sat proudly in her wheelchair at the old Boston Garden to watch one of her children compete for a state championship. Stephanie, still a teenager, had to grow up fast.

“You never fully heal from it,” she said. “I think it kind of gave me the drive to be a leader. Step up and do something to run the show.”

O’Sullivan starred at Providence College, where her team won four consecutive ECAC hockey championships from 1992-95. She was Rookie of the Year her first year and Player of the Year her last. She finished with the most assists in school history and is second in points and goals. She was inducted into the Massachusetts Hockey Hall of Fame in 2008.

“I was highly skilled but also very aggressive, very physical,” she said.

She played for Team USA in four World Championships (1994, ’97, ’99, and 2000).

O’Sullivan keeps no scrapbooks and has no favorite hockey moment. She had three assists in the third period of a 6-0 drubbing of China in 1999. The following year, she scored two goals against the Russians in a 15-0 victory for Team USA. But she mentions nothing.

“I can’t remember one in particular,” she said.

She has even lost her ECAC championship rings.

“My 16-year-old nephew asks, ‘Can I see your rings?’ I don’t know where they are,” she said. “What’s important to me are the banners that are up in the [Providence College] rink. Not rings.”

In perpetual motion

O’Sullivan dreamed of being a police officer from the time she was a little girl but she knew the clock was ticking on playing world-class hockey.

“That’s what I always wanted to do, but I kept making all these national teams,” she said.

During her career with the US national team, she had 10 goals and 13 assists in just 20 games. But in a complete shocker, she was the last player cut from the US women’s Olympic team that went on to win gold in Nagano in 1992.

“It’s water under the bridge, it’s not anything I look back on,” said O’Sullivan.

The coach of that team, Ben Smith, praised O’Sullivan.