Last year, Claire Fahey grew tired of winning so easily. No woman could compete with her in the game of real tennis—the centuries-old racquet sport that gave rise to the modern game—so she lobbied the sport’s governing bodies to let her compete in men’s tournaments. She is now preparing to enter the European Open, early next month, having proven herself a dangerous opponent to all but the top-tier men.

Real tennis is and will likely always be a niche game. It is more or less unchanged from its heyday, which lasted roughly from the sixteenth century to the eighteenth. Then, it was a populist sport, played by men and women, rich and poor. Courts abounded. After centuries of decline, sealed by the invention of modern lawn tennis, in 1874, a dwindling number of devotees kept real tennis alive, mainly in the United Kingdom, where it was played by men at tony private clubs, public schools, and on the grounds of stately homes. There are now just forty-three courts in the world; nine of them are in the U.S. But the game is slowly becoming more inclusive, as it must, in order to survive.

It is healthiest in the United Kingdom, where there are twenty-seven real-tennis courts, some of them hundreds of years old. Fahey, who is twenty-four, happened upon the sport at age eleven, when her family moved near the Prested Hall sports complex in Essex, England, which has two real-tennis courts. “We’re a pretty sporty family,” she said. “Dad brought the whole family down and said, ‘We’re all going to try this game.’ There are seven of us and five of us play. My sister is the ladies world number two and I play doubles with her.”

Though scored like lawn tennis—love, fifteen, thirty, forty, deuce, etc.—real tennis has a dizzying assortment of additional rules that can make the sport difficult for casual viewers to comprehend. Take the “chase,” for example. When a ball bounces twice, a point isn’t necessarily awarded. Instead, the ball’s second bounce on the ground is noted, and, once the players have switched sides, the point is replayed, and the receiving player tries to place a second bounce closer to the back wall than his or her opponent did.

The court, meanwhile, is lined with potential traps. There are sloping roofs above three of the four walls, for instance: you can hit the ball off of these. There are windows you can hit the ball into, a move that forces a variety of outcomes. Players like to say that real tennis is a mix of squash, lawn tennis, and chess, because of the seemingly limitless situations that can arise during a game. You serve from one side of the court, but you can win serve in the middle of a game and retain it indefinitely—and since retaining serve is crucial, players will often strategize around changing sides (which happens only when a chase is created), even if it means giving their opponent easier scoring opportunities later in the game.

Fahey relies on the consistency of her ground strokes. Real-tennis balls are made of shredded cork, covered with felt, and sewn up by hand; they are heavier and have a lower bounce than a lawn-tennis ball. They skid quickly through the hitting zone, making them difficult to strike cleanly with the small head of a hefty, wooden real-tennis racquet. “I’m not going to belt someone off the court,” Fahey said during a break between matches at the U.S. Professional Singles tournament, at the National Tennis Club in Newport, Rhode Island, in June, where she was the first female participant ever. “That’s never going to be my style, especially against the boys.” Fahey is nearly six feet tall and accents her tennis whites with bright orange or purple sneakers. “My tactic is to force them to make unforced errors,” she said.

Amateur real tennis has a handicapping system in which the better player is docked points, so Fahey has been able to challenge boys and men since she was thirteen. (There weren’t many girls her own age to play.) By the time she started playing competitively, the ladies’ events were sparsely populated and quickly became a bore, she said. She estimates that about twenty per cent of all real-tennis players are women now, up from just a handful in the nineteen-seventies, but the women who do play competitively are generally “amateurs,” meaning that they have day jobs and don’t train full time like Fahey does. (Most top male real-tennis players are teaching professionals. Fahey, who works at the Holyport Real Tennis Club in Berkshire, England, says that she is one of only two full-time female teaching pros in the sport.)

“I’m not going to say it’s a waste of time,” Fahey said of the women’s circuit, where the prize money is often paltry, “but there’s a lot of money and effort going into it**,**** **and winning easy titles, that’s not really what I’m into.”

Fahey noticed that women were not explicitly prohibited from competing in the premier tournaments against men, and last November the International Real Tennis Professionals’ Association—which governs the sport’s rankings and advocates for players to the various national governing bodies—asked the U.K.’s Tennis & Rackets Association to allow her into the 2014 British Open. There was some pushback, Fahey said, including comments that carried a whiff of sexism: some wondered whether men would be willing to compete against women, while others expressed concern for her safety. What if she were struck with the ball? “If I get hit, it’s my fault,” Fahey said. “There are worse people than me playing. They should be worried.” Ultimately, the Tennis & Rackets Association ruled in Fahey’s favor, noting that an “overwhelming majority of stakeholders” supported her inclusion, and also that the sport could face “reputational consequences” if women were barred from the leading events.

The United States Court Tennis Association subsequently found nothing in their bylaws prohibiting women from competing against the men, and Fahey did so at the U.S. Open, in February. “Claire essentially has no competition in the women's game,” the U.S.C.T.A. President Jeremy Wintersteen said. “Some say Claire is an anomaly. I hope they're wrong and that other Claires will appear and start to beat the top men.”