“There’s so many people out on tour right now who are obviously doing super well at 17 or 18 years old,” said O’Sullivan, whose first name is pronounced HAH-nah. “But I realized for me a college experience is really important, and I didn’t really see the reason to push past that.”
O’Sullivan was speaking during a break in an afternoon hitting session at Whirlwind Golf Club, near her home in the Phoenix suburbs. It was three days after she missed the cut in her first competition in several months, the L.P.G.A. Founders Cup in Phoenix, and the temperature had climbed into the mid-90s. At the start of her practice, O’Sullivan was the only person at the back of the spacious range.
Almost an hour into her session, she got company when a middle-aged man set up next to her, so close he nearly scattered the loose golf balls in her pile every time he stepped back to admire his shot. O’Sullivan kept her head down and progressed through the clubs in her bag.
Golf suits O’Sullivan because it combines her two great loves: math and self-improvement. Living in Northern California, she took her first lessons at 6; her parents signed her up on a hunch after noticing her endless enjoyment of putt-putt courses with their dragon mouths, drawbridges and windmills. She beat her father, a recreational player, at 7 and won her first tournament at 8.
At 12, O’Sullivan became the youngest winner of the California Junior Girls state championship and advanced to the match-play portion of the United States Women’s Amateur. Three years later, her mother, Sarah, said, O’Sullivan informally committed to the University of Southern California and Coach Andrea Gaston.
The 2015 season was the booster rocket that launched O’Sullivan’s career into the stratosphere. In February, she received a sponsor’s exemption for the Gateway Classic, an event on the Symetra Tour, a rung below the L.P.G.A., held at Longbow Golf Club in Mesa, Ariz., an easy drive from where the family now lives.
Bob McNichols, the general manager at Longbow, said O’Sullivan’s inclusion was not embraced by everybody.
“It was questioned by L.P.G.A. officials who wanted to be sure I knew what I was doing,” he said in a telephone interview. “They wondered whether this 16-year-old who was getting the exemption was qualified to compete in the field.”
The officials should have been worried about everyone else. O’Sullivan won by four strokes, whittling three strokes off the tournament record in the process.
“She proved herself,” McNichols said of O’Sullivan, who was the youngest winner and the first amateur to win an event on that tour since Kellee Booth in 1999.
Six months later, O’Sullivan won the United States Women’s Amateur to complete what McNichols called “the year of Hannah.”
What would she do for an encore? The pack of agents, insiders and sponsors that follow the scent of money had advice to offer. For O’Sullivan and her parents, accustomed to keeping their own counsel, the chorus of so many voices became overwhelming.
“Lots of people that mean so well, they try and give advice,” O’Sullivan said. “There’s always a lot of voices, I think, even within myself.”
Last April, O’Sullivan informed Gaston that she would not be attending U.S.C. Gaston, through a university spokesman, declined to comment. With college out of the picture, O’Sullivan prepared for the L.P.G.A. qualifying school last fall. She played in the United States Women’s Open and the Women’s British Open, and paid more attention to her surroundings. She viewed the professional landscape not as a tourist, the way she had before, but as a potential inhabitant.
O’Sullivan wondered how she would make lasting friendships in an environment where competition can trump collegiality. She noticed for the first time the quiet desperation of those in the shadows trying to eke out a living playing golf, and it gave her pause.
At first she kept her misgivings about turning professional to herself.
Her father, Greg, said: “She does worry about letting down her parents, disappointing us. She does overworry about that sometimes.”
As last summer was giving way to the fall, O’Sullivan finally gave voice to her unease. Her mother recalled a conversation in which O’Sullivan said, “I dreamed of being in college and making lifelong friendships, and now because of my success in golf I’m losing that dream?” Her mother added, “She was confused.”
O’Sullivan enjoyed school and took pride in stringing together straight A’s.
“I realized I have these two passions: learning and golf,” she said. “Ever since I was a kid, I’ve always had a really good balance between academics and golf, and I didn’t want to miss the amazing opportunity to be able to play college golf and sit in a classroom with people that they all have something that they’re great at.”
In October, O’Sullivan withdrew from the second stage of L.P.G.A. qualifying and recommitted to college. She asked her parents if she could expand her search beyond her initial choice, U.S.C., because, as her mother explained, “She’s a different person than who she was at 15.”
By the end of the year, O’Sullivan, the No. 2 female amateur, had settled on Duke, where she will join top-ranked Leona Maguire, who will be a senior when O’Sullivan is a freshman. Dan Brooks, the women’s coach, declined to comment, citing N.C.A.A. rules that prevent him from discussing incoming student-athletes until after the April signing period.
Karen Stupples, a former Women’s British Open champion who attended Arkansas State and Florida State, applauded O’Sullivan’s about-face.
“Pro golf will be there,” said Stupples, a reporter for Golf Channel, which is airing the ANA Inspiration. “If you’re good, you’re not going to fall off the face of the earth in three or four years’ time.”
Stupples added: “She should enjoy her golf and enjoy playing amateur golf, enjoy the experience of going to college. Learn everything about life, about living on your own in the college environment, and it will really help her for when she turns pro because she’ll be self-sufficient.”
Stupples’s colleague Judy Rankin, a World Golf Hall of Fame member who joined the L.P.G.A. Tour at age 17, added a caveat. “You are taking that little gamble that you’re never going to get hurt, and that you have this time to spare,” she said.
When O’Sullivan decided to put off her career by taking this gap year “there was fear, for sure,” her father said. He added that the extra time they had together as a family had been “awesome.”
In February, they traveled to South Korea, where O’Sullivan’s mother’s family is from, a trip they had put off repeatedly because they could not wedge it into O’Sullivan’s golf and school schedule. The day after O’Sullivan missed the cut in the Founders Cup, she and her mother took her father out to lunch to celebrate his 51st birthday.
Greg O’Sullivan became emotional when he talked about the twists and turns in his daughter’s journey.
“I’m really proud of her for speaking up about what was important to her at a time when agents and potential sponsors were pursuing her,” he said. With his voice cracking, he added, “There’s no handbook for guiding an overachiever like Hannah.”