Guadalajara, Mexico, gave a party for women’s tennis last month, and when it ended, with Garbiñe Muguruza winning the WTA Finals, the season’s last tournament, confetti fell through the air and a mariachi band turned the Akron Tennis Stadium into a fiesta.

In the middle of it, Steve Simon, the bespectacled chairman and chief executive of the WTA Tour, stood quietly and unsmiling in a blue business suit with his hands clasped. He shared the occasional quiet word with Chris Evert and Billie Jean King, or one of the local officials he had helped persuade into holding the event on short notice, after the regular host, Shenzhen, China, pulled out because of the pandemic.

Simon had plenty else on his mind. As the tournament and closing celebration unfolded, a geopolitical crisis with women’s tennis at its center had occupied much of his time and he was leading the tour down an uncertain path.

On Nov. 2, the Chinese tennis star Peng Shuai accused Zhang Gaoli, a former vice premier of China, of sexually assaulting her in social media posts that were quickly deleted.

The Chinese government removed all mentions of Peng’s accusation, and coverage of Peng from news media outside China has been censored. She largely disappeared from public life, and Simon has been unable to communicate with her despite repeated attempts.

On Nov. 13, Simon went public with his frustration, demanding that he and the WTA be able to speak with Peng independently and that Chinese officials conduct a transparent investigation into her allegations. If they did not comply, Simon said, the WTA would consider removing its nine tournaments from China, including the Tour Finals, moves that could cost women’s tennis tens and perhaps hundreds, of millions of dollars over the next decade.

On Wednesday, Simon followed through on his threat, announcing that after weeks of failed attempts to communicate with Peng, and no sign of an investigation or evidence that Peng can speak freely, the WTA was immediately suspending all of its tournaments in China. Simon’s stridency, in contrast to other international sports leagues and organizations that do business in China, has turned Simon, a mild-mannered former tournament director who prefers to operate in the background and leave the spotlight to his star players, into the most talked-about leader in sports.

“This is not where I wanted to end up,” Simon said in an interview Wednesday night, speaking about the WTA Tour, but also, in a sense, about himself.

“I don’t want this to be about me,” he added. “Nothing prepared me for it, other than just trying to do what is right and communicating that with the players.”

Simon’s refusal to accept China’s authoritarian stance on human rights once it directly affected one of his players stands in stark contrast to several high-profile leaders in sports who have repeatedly bent to the desires of the Chinese, including Adam Silver, the commissioner of the N.B.A., and Thomas Bach, the president of the International Olympic Committee.

Simon has been concerned about Peng’s physical safety but also believed, as did the members of his player council and others he communicates with regularly in a player chat group, that the silencing of Peng and her sexual assault allegation amounted to a direct attack on the principle of equality upon which the WTA was founded.

“It’s now December and we’ve not seen any meaningful progress,” he said Wednesday night.

Simon, a 66-year-old Southern California native, played tennis at Long Beach State University and mixed doubles at Wimbledon in 1981 alongside Lea Antonoplis. He has spent his adult life in tennis coaching, running the tennis program for Adidas, and organizing and eventually directing the BNP Paribas Open, a joint men's and women’s event in Indian Wells, Calif., known as the fifth Grand Slam.

All along, Simon was quietly gaining authority within tennis circles, even if few of the players knew him particularly well. He began serving on the board of the WTA in 2004.

In 2009, he worked to get Stacey Allaster, then the president of the WTA, appointed as the next chief executive. Allaster said during a rough moment for her candidacy, she privately asked Simon if he might be a better fit to lead the organization.

“Without a blink he turned to me and said, ‘No, we’re going to stay the course,’” Allaster said.

Six years later, after Allaster decided to step down, the WTA board unanimously selected Simon to succeed her. He has since cultivated the support of the sport’s biggest stars of the present and past, including Serena Williams and King, the founder of the WTA, while maintaining his decades-long relationships with the tournament directors who were his initial base of support.

“He’s a rarity in sports,” said John Tobias, a prominent tennis agent who represents Sloane Stephens, the 2017 U.S. Open women’s singles champion. “An executive who is always trying to put the focus on the tour and the players.”

Before this month, Simon was best known for the work he performed behind the scenes, along with the former pro Charlie Pasarell and others, to bring Venus and Serena Williams back to Indian Wells after a 14-year absence. Serena Williams was ceaselessly booed by fans after her sister withdrew from a semifinal match between them. Williams believed that race had played a role in how fans treated her. She said at the time that Simon spent a long time listening to what she had to say on the matter and that played a major role in her decision to return.

Simon was also outspoken behind the scenes in 2009, when the government of the United Arab Emirates denied a visa to Shahar Peer, an Israeli tennis player, because it did not recognize the State of Israel, Allaster and others involved with the situation said. In board meetings with the WTA, Simon, who led the representation of the tournaments, pushed the WTA to threaten to pull the tournament from the U.A.E. unless it granted access to Peer the next year, even though that meant going against an entity he was supposed to represent. Peer received entry the following year.

Simon spent his first years leading the WTA leaning into his tendency to remain in the background, even as the organization achieved record revenues, thanks in some part, to its expansion into the Far East, specifically China. The country had undergone something of a tennis boom following the success of Li Na, who won the French Open women’s singles title in 2011, and Peng, who became the world’s top-ranked doubles player in 2014. Setting aside concerns about human rights so long as its players were treated well, as nearly all major sports have done, the WTA in 2019 began a 10-year deal to hold its season-ending championship in Shenzhen, with promised prize money of $14 million annually.

Over the past two years, Simon has managed through the sport’s shutdown and declining revenues in its return during the pandemic. The crisis involving Peng is his greatest challenge yet.

In February in Australia, Johanna Konta, the recently retired British pro, was asked what she had learned from her time on the WTA Player Council. “Mostly I’ve learned just how hard Steve Simon works,” Konta said.

Through it all, Simon has relied on near constant communication with players and tournament officials, including video calls and digital group chats with select players.

Pam Shriver, the retired doubles champion who is now a commentator for ESPN, said during the shutdown Simon held weekly video calls with the players and often invited retired greats, such as Shriver, Evert, King and Martina Navratilova to give moral support and explain to the younger generation that the tour had survived tough times before, like when it broke away from the men’s game in the early 1970s, or when it parted with its sponsor, Virginia Slims, without having a clear replacement.

“What he realizes is that sometimes you make tough decisions and sometimes you don’t know how they will work out,” Shriver said.

Simon explained that he had chosen the word “suspension” to signify his hope that China would eventually accede to the WTA’s demands for Peng to speak freely and for an investigation to take place.

He is also hunting for new investors and sponsors who can help replace the prize money and revenue that the tour stands to lose by abandoning the world’s most populous country, a lucrative but complicated market.

“I will continue to reach out and use every avenue available to get this to an appropriate resolution,” he said. “If it ends up that not being their preference, then we will not be operating in the region.”