Swimmer Sun Yang, right, from China, arrives for a public hearing at the Court of Arbitration for Sport (CAS) in Montreux, Switzerland, on Nov. 15. (Keystone via AP)

MONTREUX, Switzerland--One of China’s biggest Olympic stars fought Friday for his right to compete at the 2020 Tokyo Games during a rare public hearing that turned combative at times, as champion swimmer Sun Yang defended his refusal to complete a doping test last year.

During a 10-hour session marred at times by translation problems, Sun maintained that inspectors drawing blood and urine samples failed to have proper identification papers.

The interpretation issues in both English and Chinese brought a halt to the landmark Court of Arbitration for Sport hearing several times, frustrating lawyers for both sides during Sun’s opening cross-examination. Sun’s mother later took the stand, at one point admonishing lawyers, “I haven’t finished yet.”

One lawyer said he could not tell if Sun was being evasive or if it was simply a case of misunderstood translation.

The case stems from the three-time Olympic champion’s refusal to cooperate with three anti-doping officials during a random test that became a confrontation in the early morning hours at his home in China in September 2018.

“During inspection, I realized they don’t have any authorized papers to prove their identification,” Sun testified Friday.

A World Anti-Doping Agency expert disputed Sun’s account, saying the inspectors’ credentials were in order.

A tribunal appointed by the swimming world body FINA initially gave Sun only a caution, but WADA appealed the case to CAS. Its judges are not expected to hand down a verdict until next year. If the ruling goes against him, Sun could be banned from the 2020 Olympics.

The 6-foot, 7-inch (2-meter) Sun became a star in China as the country’s first man to win an Olympic title in swimming. He won gold medals in the 400- and 1,500-meter freestyle races at the 2012 London Olympics. He added gold in the 200 at the 2016 Rio de Janeiro Olympics.

The 27-year-old Sun, who also has 11 world championship titles, has been a polarizing figure in the sport.

In Rio, one Australian rival called him a drug cheat as anger built over a three-month ban for his positive test in 2014 that some considered too lenient. The ban was initially kept secret by Chinese authorities and FINA, which some accused of appearing to protect one of its biggest names in a key market.

Sun provoked more anger among rivals by winning two world titles in July while the CAS appeal was pending. Medalists from Australia and Britain refused to stand on the podium with him in Gwangju, South Korea.

The translation problems at Friday’s hearing began almost from the start, and it was unclear at times how much of the testimony and questions were understood, with both judges and lawyers expressing frustration.

At one point, Sun’s Geneva-based lawyer, Ian Meakin, apologized for asking his client leading questions, saying: “The translation was so bad.”

The translation was so poor that “you couldn’t tell if (Sun) was monumentally evasive or couldn’t understand the questions,” said Richard Young, a lawyer for WADA.

When the hearing resumed after a break, judging panel president Franco Frattini also apologized for its poor quality.

The court noted that Sun’s team selected the translators, who were replaced at a lunch break by a WADA staff member. Lawyers were told an accurate transcript of the morning sessions would later be provided to all parties.

Sun detailed how he and his entourage had doubted the qualifications of the officials conducting the doping test at his home.

“How are you able to trust them?” said Sun, whose personal doctor had been summoned to the scene.

A security guard, under instructions from Sun’s mother, used a hammer to smash a box containing a vial of his blood during the late-night dispute after the swimmer questioned the collection team’s credentials.

Sun said he was not respected by the officials, including a chaperone he said asked to take his photograph.

“This is really ridiculous,” Sun said in translated comments.

Although Sun and his entourage were criticized for their conduct, the first FINA tribunal panel said the sample mission was void and invalid because anti-doping protocol was not followed. Technically, Sun was judged to be not properly notified of needing to give samples.

WADA has asked for a ban of between two and eight years, saying Sun voluntarily refused to submit to give samples.

“That is pretty sensational,” Young, the WADA lawyer, said of the hammer-smashing incident. “But he was nailed on a tampering violation before any of that happened.”

If WADA’s appeal is upheld, Sun risks a longer sanction that could bar him from the Tokyo Games because it would be his second offense. The first offense brought the three-month ban imposed by Chinese authorities in 2014, after Sun tested positive for a banned stimulant.

That initial ban was quickly addressed by Sun and his legal team on Friday. He said it was a prescribed medication for a heart issue because he sometimes fainted after training.

Lawyers for WADA repeatedly asked if Sun had learned in his long career of the serious consequences for refusing to give a sample. He repeatedly answered that the lead anti-doping official had not warned him specifically.

Sun’s anti-doping history was detailed, with 180 samples given at competitions and during training from 2012-18. A total of 60 were organized by the Sweden-based firm IDTM, which sent the collection team to Sun’s home in 2018.

CAS judge Philippe Sands pressed Sun about whether IDTM staff had shown different kinds of documents of authorization on the 59 previous occasions he gave samples without problems.

Friday’s hearing, the first open to the media and public observers since 1999, played out inside a ballroom annex set among lakeside hotel gardens in the upscale Swiss resort of Montreux. Next door stood the concert halls of the city’s famed jazz festival.

Amid concerns over witness intimidation, the three anti-doping officials who visited Sun’s home testified earlier and did not attend Friday’s session, which was watched by more than 100 accredited observers in the room and streamed live on the CAS website.

The hearing ended with Sun surprising his own legal team by waving his arms and calling another translator from the public seats to better articulate his closing statement.

“Who is this guy?” asked an incredulous Judge Frattini, a former Italian foreign minister. “It is not up to you to appear before the court.”

“There are some rules,” he said.