Simona Halep first picked up a racquet when she was four years old. At fourteen, she decided to dedicate her life to tennis. At sixteen, she left her family, in the small, ancient city of Constanta, Romania, and moved into a hotel in the capital, Bucharest, in order to train at a serious academy. Her father jokingly called her his “little Rolex,” because, at a young age, she told him that she would win the big tournaments. At seventeen, she had breast-reduction surgery—a frightening procedure, which lasted nearly seven hours—in order to relieve pain in her back and help her game. As a child, Halep was so shy that it was painful for her even to speak on the phone, but she forced herself to face the cameras and the scrutiny of the media, which grew more intense with each season. Every day, she went to the gym to tend to her muscles, joints, and ligaments. When her friends went to parties, she went to sleep.

She had talent to match the work ethic: she won the junior French Open in 2008, at the age of seventeen, turned pro, and broke into the Top 100. But it was not obvious that she would ever reach the top ten. Halep is small for a tennis player—she’s only five feet six—and she lacked a big serve and blistering shots. The larger problem was that she would sometimes fall apart. She went nearly a year, from May of 2012 to March of 2013, without winning two matches in a row. The Times once described one of her matches as “mesmerizing, like any passing calamity.”

Then, in 2013, she started to win—six titles that season. That was when I started watching her, and I, like the Times, found her game mesmerizing, though for different reasons. Halep had peerless stamina and speed, and played with perfect technique. Her sloping shoulders became muscular, and her legs strong; her feet were light and quick, always moving. She dug sure winners out from far corners. She had an instinct for the geometry of the game, carefully constructing her points. Her forehand was clean and metronomic, her backhand powerful and poised. When she hit it perfectly down the line, you could see the pleasure it gave her, as though she were a singer settling into a high note. Likewise, when she faltered, the air around her seemed to vibrate with despair.

As for her sudden success, there were the usual factors: good health, a new coach, a more aggressive mentality. She said that she had become more relaxed, and was enjoying the game. She had a newfound belief in her ability to challenge the top players. Whatever it was, it looked like an awakening. Her eyes, wide-set and hazel, radiated a rare intensity.

In 2014, at twenty-two, she made it to the final of the French Open. She racked up big wins over top players, including an in-form Serena Williams, and rose to No. 2 in the world. The following year, she won Indian Wells, a tournament at the level just below the majors. She was a contender on any surface. “She’s one of the toughest people I could ever play,” Naomi Osaka, the current No. 1, and the reigning Australian and U.S. Open champion, told me. “She moves really well, and she fights for everything.”

But then, in 2015 and 2016, Halep’s performance seemed to plateau. She was often too willing to hang back and react; she also seemed to be wrestling with her ambition. Whatever sense of freedom had fuelled her rise was forgotten as success bred new expectations, from herself and others. There was the pressure to justify her many sacrifices, and the desire to fulfill her country’s hopes. “Simona is without a doubt THE biggest sports star in Romania,” Adrian Toca, a Romanian journalist, told me, in an e-mail. The coverage was relentless, and not always kind. Small armies of fans come to see her in Doha, Toronto, and Ohio, wrapped in flags. She often fed off their support, and she drew strength from a wellspring of passion. She was so fiery that the commentator Brad Gilbert nicknamed her Halepeño—but her negative emotions could overwhelm her. She would kick the air, scream at her coach and the supporters in her box, swipe her racquet, berate herself. It was alternately thrilling and heartbreaking to watch, as an internal struggle played out on her face, in the set of her shoulders, in the depth of her shot and the placement of her serve. Occasionally, she seemed simply to give up. “She became her worst enemy quite often,” Darren Cahill, who was Halep’s coach from 2016 until the end of 2018, said. “She fought more than one opponent,” he added—there was the player across the net, the people in her coaching box, and herself.

Tennis is a psychologically taxing sport. There are no teammates to rely on, and a coach can’t call timeout when things are going wrong. Tournaments are single-elimination, so there is no way to make up for one bad day. The mechanics of the game can be as much mental as physical: the slightest hesitation will mean a ball flies long; during a serve, stress can make an elbow drop. There is no model for how to handle the pressure. Some players smash racquets. Some can tune everything out. Roger Federer can get over a loss in ten minutes. The greatness of Serena Williams, on the other hand, depends partly on a desire to avenge her few losses.

Halep dreams of playing with the easy touch and the attacking genius of Federer—if she could play like him even “for one point,” she told me recently, “then I would be super happy.” But her game is more like that of Novak Djokovic, mentally and physically crushing. “We like to stay on the baseline and just to kill the opponent, to make him suffer,” she said. In the past, though, she was sometimes the one who seemed to be in agony. “There comes a moment when it’s like she sees this hawk over her head that no one else can see,” Mary Carillo, a commentator and former professional player, told me. “Her matches would take on this doomed quality. And you could watch it!” Halep makes the psychological complexity of sports, the interplay of courage and fear, and of ease and intensity, visible as few athletes do. It’s gripping to see.

When Cahill began coaching Halep, in 2016, she was a classic counterpuncher. She settled behind the baseline, retrieving shots. This usually worked; she could frustrate opponents, baiting them to go for too much, and she could use their power to produce her own. But the style was physically punishing for her, too, and she was vulnerable to getting hit off the court. The fix, to many observers, seemed obvious: she needed to step inside the baseline and play more aggressively. But she’d never been comfortable playing that way.

Cahill, who previously coached Andre Agassi and Lleyton Hewitt, understood that he wasn’t going to change Halep’s nature. Rather than fight her instinct to hang back, Cahill worked on introducing variation to her game, to “open up the court a little more,” he told me, to “zig-zag behind the baseline instead of standing six feet back.” They worked on her transitions to the net, so that she would have the tools to play that game, even if the forecourt would never feel like home. During practice, he had Halep hit drop shots ad nauseum. They analyzed her matches together on YouTube, to study what she could improve. Before, Halep had believed she played best instinctively. Now they came into each match with a plan.