Sun Yang celebrates winning the men's 400-meter freestyle at the world swimming championships. (Antonio Bronic/Reuters)

GWANGJU, South Korea — When he touched the wall and removed his goggles following his opening race of the FINA world championships, China’s Sun Yang waved his index finger for the crowd. The message was clear, and no translation was necessary: No. 1.

A three-time Olympic champion, Sun is comfortably atop the world rankings, a podium threat every time he hits the water. He won his first gold medal at these championships Sunday and probably will add more to his bountiful collection of world titles this week. He is widely regarded as the best swimmer China has ever produced, but for many around the sport, Sun is also Public Enemy No. 1, a cloud of suspicion following him around the pool deck and the latest sign that swimming is still plagued by doping problems that the sport has struggled to rein in.

Sun is accused of smashing a vial of blood with a hammer last year, preventing anti-doping testers from taking a sample from his home. FINA, the international governing body for the sport, issued a warning to the swimmer, but the World Anti-Doping Agency is seeking a tougher punishment from the Court of Arbitration for Sport. The CAS hearing isn’t scheduled until September, and FINA gave Sun the green light to compete this week in Gwangju. His mere presence at the year’s biggest meet has created a stir around the pool.

“Personally, I am not remotely comfortable with FINA’s approach to doping control,” American swimmer Lilly King said.

There are 1,200 swimmers competing here but none as controversial as Sun. He is entered in the 200-, 400- and 800-meter freestyle races this week and opened the meet by winning the 400 with a time of 3:42.44, becoming just the third swimmer to win four world titles in the same event. The win is his 10th individual world title, tying him with Ryan Lochte for the second most among men, trailing only Michael Phelps, who had 15.

Sun, 27, has maintained his innocence and defended smashing the vial. His legal team said the drug testers “were not properly accredited to carry out the out of competition tests” and one of them “was secretly filming [Sun] without his permission.”

Now that FINA has allowed the Chinese star to race, many of his competitors are guarded with their words.

Australia’s Mack Horton finished second to his rival Sunday, 0.73 seconds away from a gold medal. After the race he said he was frustrated and told reporters, “I think you know in what respect.” Horton declined to shake hands with Sun on the medal podium or stand next to him for photographs. FINA later sent a warning letter to Swimming Australia Ltd. and to Horton and said in a statement, “While FINA respects the principles of freedom of speech, it has to be conducted in the right context.”

“His actions speak louder than anything I’ll ever say,” Horton said.

Said Italy’s Gabriele Detti, the third-place finisher: “If he’s here, he can [swim], so I try to beat him. … All the rest, I don’t care. “

They’re all aware of the history and speculation that surrounds Sun but have no recourse. FINA made its ruling, and only CAS can take further action.

“If you do step back and you hear or read the chatter or listen to what’s going on, yes, you want more to be done,” said Dave Durden, the U.S. men’s coach.

As a coach, Durden’s goal is to get his athletes to swim as fast as possible, and he can only hope it’s against a clean field. “That’s all we want,” he said. “It’s a pretty simple request. … I think they owe that to these athletes who are working their tails off to have the competition be a level playing field when it comes to drugs and doping.”

FINA’s decision to allow Sun to compete hasn’t inspired confidence across the pool deck. Few have been more outspoken than King, a two-time Olympic gold medalist.

“I think all of us would say that we’re racing dopers at some point,” she told reporters before the meet began, “and we shouldn’t really have to say that.”

Asked what FINA could do better, King didn’t mince words. “They could start with not letting people who have smashed blood vials in tests compete in their meets,” she said. “I mean, that’s really sketchy and pretty insane that that’s happening."

King has a history of speaking out about doping issues. At the 2016 Olympics, she made headlines by saying that Russia’s Yuliya Efimova should have been barred from competing. Efimova had served a doping ban but was allowed to swim at the Rio Games following a favorable CAS ruling.

WADA has its testers at these world championships, which means Sun and many others will have to submit fresh samples, both at the pool and at the athletes’ village. The swimmers know it’s essential to ensuring fair competition. Within an hour or so of arriving in Gwangju last week, in fact, several U.S. swimmers were immediately subjected to random drug testing.

“Even if they show up at 11 at night or 6 in the morning, as annoying as it is, I have to welcome that because I know I’m doing it clean,” said Caeleb Dressel, who’s trying this week to match his seven titles won at the 2017 world championships. “And I think it’s good for the sport. … The sport has to be clean. There has to be an even playing field between everybody. If a drug tester shows up at my door at 3 a.m., I have to welcome that.”

The issues aren’t new and aren’t limited to swimming. Even as they loom in the background of most major meets, the clock isn’t swayed by the whispers and rumors around the pool deck. Sun will post his times and win his medals, and CAS probably will have the final say on the matter. Everyone else competing at the world championships will try to focus on posting the best times they can.

“At the end of the day, I can’t control what someone else is putting in their body,” Dressel said. “I can control what I’m doing. ... I’m just going to focus on myself and Team USA.”

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