Chinese Olympic gold medallist Sun Yang has been banned from swimming for eight years for breaking anti-doping rules, but the swimmer has indicated he will appeal the Court of Arbitration for Sport's (CAS) ruling.

Key points: Sun has been banned from swimming until February 2028 for refusing to cooperate with sample collectors

Sun has been banned from swimming until February 2028 for refusing to cooperate with sample collectors The ban means Sun will be unable to defend his 200-metre freestyle title at the Tokyo 2020 Olympic Games

The ban means Sun will be unable to defend his 200-metre freestyle title at the Tokyo 2020 Olympic Games Sun was the first Chinese swimmer to win Olympic gold

The CAS found the three-time Olympic champion guilty of refusing to cooperate with sample collectors during a visit to his home in September 2018 that turned confrontational.

In a rare hearing in open court in November, evidence was presented of how a security guard instructed by Sun's mother used a hammer to smash the casing around a vial of Sun's blood.

FINA's doping panel had cleared Sun of any wrongdoing in the incident but the World Anti Doping Authority (WADA) appealed that decision.

The swimmer had asked CAS for a public trial.

A 10-hour hearing broadcast on the court's website was hampered by severe translation issues between Chinese and English.

Australian Mack Horton refused to stand on the podium with Sun Yang at the FINA World Championships last year. ( Reuters: Kim Hong-Ji )

The CAS panel's verdict was delayed until all parties got a verified translation.

Sun responded to CAS's decision by saying he would "definitely" appeal the ruling.

"This is unfair. I firmly believe in my innocence," the 28-year-old Sun was quoted as telling China's official Xinhua News Agency.

"I will definitely appeal to let more people know the truth."

Jack Anderson from the Melbourne Law School said Sun's last avenue of appeal was to the Swiss Federal Tribunal.

"It's very difficult to succeed there. There are very narrow procedural grounds," Professor Anderson told The World.

"His main ground throughout all of this is with anti-doping policy [there is] strict liability against the athletes, but it should equally be strict liability against the testers and the administrators. And he feels that that principle has not been upheld."

Sun, the first Chinese swimmer to win Olympic gold, has long been a polarising figure in the pool.

The Chinese swimmer came to the attention of Australians after Mack Horton led a protest against Sun at the Rio Olympics in 2016.

Horton and Scottish swimmer Duncan Scott refused to stand with Sun on medal podiums at the 2019 FINA World Championships in South Korea.

Ban puts swimming career in doubt

The long ban almost certainly spells the end of Sun's career.

Now banned until February 2028, Sun cannot defend his 200-metre freestyle title in Tokyo.

WADA went to CAS after a FINA tribunal only warned Sun.

Sun Yang had asked for a public trial. ( Reuters: Denis Balibouse )

The first ruling was that anti-doping protocol was not followed, making the samples invalid, and cited doubts about credentials shown to him by the sample collection team.

WADA requested a ban of between two and eight years for a second doping conviction.

Sun served a three-month ban in 2014 imposed by Chinese authorities after testing positive for a stimulant that was banned at the time.

The ban was not announced until after it ended and he never missed a major event.

That first case led to criticism of FINA for appearing to protect one of the sport's biggest stars in a key market.

Calls for medals to be reissued

British Olympic silver medallist Sharron Davies questioned whether FINA was "fit to govern swimming after this cover-up" and said Horton, as well as Scott, deserved apologies.

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"Swimmers lost medals at last years' World champs that should be re-issued & apologies given to Scott and Horton," the 1978 Commonwealth Games gold medallist tweeted.

WADA said it welcomed the CAS ruling.

"WADA decided to appeal the original FINA ruling having carefully reviewed it and having concluded that there were a number of points that seemed to be incorrect under the [doping] code," WADA director-general Olivier Niggli said.

"Today's CAS ruling confirms those concerns and is a significant result. We will now need to take time to review the decision in full."

AP/ABC