What’s the Most Curious and Fraught Job in Tennis?

Consider Halep’s quarterfinal match against Amanda Anisimova of the United States set for Wednesday. For more than six years, Darren Cahill, the longtime coach and ESPN commentator, who has worked with Andre Agassi, Andy Murray and Ana Ivanovic, among others, coached Halep.

They split in September. Cahill, who is Australian, said the rigors of travel and the Covid-19 quarantines that Australia required each time he returned home had become too much. But after Australia lifted the requirements, Anisimova asked Cahill to join her team before the Australian Open in January and he obliged.

Anisimova’s main coach had been her father, who died suddenly of a heart attack at 52 in 2019. She has struggled to find a stable coach since. But the relationship with Cahill did not quite click, and Cahill split with Anisimova in March, saying he had overestimated his ability to manage the commitment to her and his family. Cahill has since signed on with Jannik Sinner, the emerging 20-year-old Italian star, who in February fired his longtime coach Riccardo Piatti, a relationship that, until the split, most figured would last for years. Sinner lost Tuesday to Novak Djokovic.

So many players seem to go through so many coaches. And yet Paul Annacone, who has coached Pete Sampras, Roger Federer, Sloane Stephens and recently began working with Taylor Fritz, said the most important thing a coach can provide a player was “stability” and what he described as a “macro comprehension of the environment and best practices to get that player to buy into an agreed-upon philosophy.”

Annacone said coach-player relationships often founder when communication breaks down. Really “knowing the other person is essential,” he said.

Or maybe, sometimes, it isn’t.

Mouratoglou and Williams were nearly inseparable for years. He was the constant presence on the practice courts with her and in her box. He even admitted to coaching her during the 2018 U.S. Open final against Osaka, a violation that led to her being penalized a point and then a game during the match, which she lost in straight sets.