Scott Whitmore stood along the concourse on a recent spring night watching the final inning of a Staten Island FerryHawks home game wind down when a New York City police officer approached him from the third-base side.

“After the game,” the officer said sheepishly, “you think I can get your daughter’s autograph?”

Sure, Whitmore chuckled, though he knew the receiving line would be long. Outside of a handful of Yankees and Mets stars, the most famous ballplayer in New York this summer might well be Staten Island’s pioneering two-way player, Kelsie Whitmore.

Standing 5 feet 6 inches, with dark chestnut hair that unfurls past her uniform number, she is impossible to mistake in the FerryHawks’ dugout, warming up on the field or signing autographs. She is an unusual sight even in a league known for taking chances and pushing buttons.

The Atlantic League of Professional Baseball, widely considered the highest level among baseball’s independent minor leagues, has hosted the former All-Stars Roger Clemens, Jose Canseco and Rickey Henderson. But a woman had never started an Atlantic League game, nor pitched in one, until Whitmore, who has done both. She’s the first woman to play in a league partnered with Major League Baseball since Lee Anne Ketcham and Julie Croteau joined the Maui Stingrays of the Hawaii Winter Baseball league in 1994.

That league was about the equivalent of Class A minor-league ball, whereas the Atlantic is thought to be closer to Class AAA, one step below the big leagues. At 24, Whitmore, a former Cal State Fullerton softball star, is making a run at sticking in professional baseball.

For Whitmore, that represents a return to normal. She played softball because it was the only way she could earn a college scholarship. But she is — always has been — a baseball player, and she shares many of the telltale traits. She wears her cap pulled low, swings a 32.5-ounce bat, curses impulsively and spits reflexively.

The tattoos on her left forearm contain Filipino imagery — an homage to her mother’s heritage — including a string of crocodile teeth, representing an aggressive hunter lurking under a quiet, tranquil facade.

“It symbolizes me,” she said, “as a person and a player.”

Whitmore has been surprising unsuspecting baseball men since she was a teenager. She was the only girl on the varsity baseball team at Temecula Valley High School in Southern California, and at 17 was one of two who were signed to play professionally for the Sonoma Stompers of the Pacific Association, an independent league.

Now, she is on her own in a league filled with former major leaguers, on a team managed by a former Mets player, Edgardo Alfonzo.

There are other women carving paths in baseball, a male-dominated sport. This spring, Rachel Balkovec of the Tampa Tarpons became the first woman to manage in affiliated baseball. In March, Alexis Hopkins was drafted by the Atlantic League’s Kentucky Wild Health Genomes to serve as the team’s bullpen catcher.

But Whitmore, who has twice started in left field and made four appearances on the mound, is making her case that she belongs on a professional baseball diamond as a player.

“That’s a groundbreaking event for us,” M.L.B. Commissioner Rob Manfred said of Whitmore. “It gives you an honest-to-God, real-life example of what we’ve been saying for years, aspirationally: Some day, we’re going to have women playing professionally for us.”

A Ponytail Protest

After a recent night game was postponed because of weather, Whitmore was at the stadium with some teammates working out and negotiating who was going to make the run for chop cheese sandwiches — a bodega specialty that has become an obsession in the FerryHawks’ clubhouse.

She suddenly stopped walking to figure out how to leap across a roughly eight-foot-wide puddle that had formed on the concrete, which she cleared with ease. “I did long jump in high school,” Whitmore shrugged.

Her athletic career has also included soccer, lacrosse, flag football and volleyball. She can clear 280 yards with her driver and dead lifts 400 pounds.

Was there any sport she hasn’t tried?

“Cheer,” Whitmore said.

Scott Whitmore, a physical-education teacher, said baseball was his daughter’s first love. At age 6, Scott brought Kelsie to register for Little League, but she refused. She was content playing catch and taking swings in the backyard.

“Finally I said, ‘Why don’t you want to play with kids your own age?’” Scott Whitmore said.

It was because she thought she would have to wear her hair in a ponytail. She preferred to leave it long.

Her dad laughed and told her she could wear her hair however she wanted. It has remained down ever since.

“I guess part of me was like, if I do have it up, I’ll just be like all the other girls,” Whitmore said. “It wasn’t comfortable. It wasn’t me.”

It’s not uncommon for girls to play Little League. But it didn’t take long before Whitmore began to recognize just how gendered the constructs were for baseball (boys) and softball (girls).

“You’d hear the doubters,” Scott Whitmore said. “‘Hey, the boys are going to get stronger, and she’s not going to be able to hang with them.’ They said that at age 12, and it never happened.”

Justine Siegal first saw Whitmore pitch when she was 15. Siegal, who was the first woman to coach for a major league organization, founded the nonprofit Baseball For All to promote gender equality in baseball and offer opportunities to girls who want to play on youth teams.

From that first introduction, Siegal kept tabs on Whitmore, thinking perhaps she could be the one to break through and advance further in professional baseball than any woman in decades.

“She had something special,” Siegal said of Whitmore. “It was clear she had the physical abilities to compete.”

But in high school, Whitmore wondered if she had the mental stamina to press on.

“I started to get that feeling of, am I not supposed to be here?” Whitmore said. “Do I not belong here? People keep asking me why I’m here, people are wondering, outsiders are trying to push me toward a different route. It started to mess with my head.”

Loneliness became a factor, too. Always the only girl, the standout, the outlier. It became draining emotionally, she said.

“You just want to know that feeling of what it is to fit in,” Whitmore said.

Unable to secure a baseball scholarship, she entered a softball recruiting showcase despite limited experience with the game. Her athleticism and her baseball instincts proved enough to attract a flood of offers from coaches who thought, within time, they could mold her into a star.

She used to recoil at the thought of switching to softball. “It just wasn’t what I wanted to do,” Whitmore said. “The high school softball team wanted me to play for them. To be honest, that’s like telling me to go play soccer. In my head, it’s a totally different sport.”

Yet college softball looked more appealing as Whitmore considered that the spotlight might not be so focused on her.

“I thought, if I go play on a team full of girls, I’ll know that feeling of not being the one everyone is always looking at or wanting to change,” Whitmore said. “When I stepped on a softball field, I was like, ‘OK, cool, I’m finally a part of them.’”

‘The Thing’

She was still different.

She moved like a baseball player, wore a hat, wore baseball pants. She had to relearn how to hit, how to judge fly balls, how to swipe bags. Even the atmosphere in the dugout was foreign to her — a roster of girls interacted differently from guys.

After games, she would slip into the batting cages to take cuts against overhand pitchers. In the summer, after the Fullerton season was over, she pitched for the U.S.A. baseball women’s national team. “I told myself, this is just temporary,” Whitmore said of softball.

She also reached out to Joe Beimel, a former big-league reliever who opened a training facility in Torrance, Calif., that helps pitchers build velocity. When Whitmore arrived, her fastball maxed out a little over 70 miles per hour.

“We needed to get her at least into the 80s,” Beimel said in a phone interview. But he was impressed with the movement on her pitches.

Whitmore’s pitching arsenal includes a two-seamer, four-seamer, slider, curve — and something else entirely. “It’s this weird knuckleball-changeup she throws,” Beimel said.

Whitmore calls it “the Thing,” and the pitch has become a source of fascination on the FerryHawks. A former teammate Julio Teheran, who previously had pitched for the Atlanta Braves, the Los Angeles Angels and the Detroit Tigers, had been studying her grip before he recently left for the Mexican League.

Whitmore will never blow professional hitters away (she now throws in the upper 70s), but Eddie Medina, the FerryHawks’ director of operations who had pushed to sign her, felt Whitmore could keep hitters off-balance.

Her pitching coach, the former major leaguer Nelson Figueroa, succeeded despite a lack of velocity, and he has helped Whitmore adapt. In her second pitching appearance of the season, she allowed six runs in two-thirds of an inning during a blowout loss. She notched a scoreless inning in a recent appearance on June 5.

Despite the mixed results, fans cheer her name and show up to see her. Life in baseball means dressing in her own locker room and showering in a facility used by the team’s coaches.

But she calls her teammates her “big brothers,” and they have reciprocated the embrace.

She also has her dad around as a source of comfort and laughter. Scott Whitmore retired in late May, packed the car and drove across the country.

He didn’t intend to miss a game. “I’m going to spend the entire summer watching my daughter play baseball.”