LAUSANNE, Switzerland -- Chinese swimming star Sun Yang was banned for more than four years Tuesday for breaking anti-doping rules after a retrial at the Court of Arbitration for Sport.

The court's verdict ends Sun's hopes of defending his Olympic title in the 200-meter freestyle in Tokyo next month. The ban is backdated to February 2020, meaning Sun could return for the 2024 Paris Olympics, when he would be 32.

The judges found Sun "to have acted recklessly" when he refused to let anti-doping officials leave his home with a sample of his blood.

Sun's original eight-year ban imposed last year for this offense was overturned on appeal to Switzerland's supreme court, which ordered a fresh prosecution.

Federal judges ruled the first guilty verdict unsafe because the chairman of the three-judge panel at CAS showed anti-Chinese bias in social media comments.

The retrial was heard by three new judges by video link over three days last month and fast-tracked ahead of the Tokyo Olympics, which open on July 23.

The case was about a failed attempt to take blood and urine from Sun by a sample collection team that made an unannounced visit to his home in China in September 2018.

It turned confrontational and led to Sun's entourage ordering a security guard to smash the casing of a blood vial with a hammer.

The World Anti-Doping Agency appealed to CAS when a tribunal appointed by swimming's governing body, FINA, merely warned the three-time Olympic champion about his conduct.

WADA requested a ban of two to eight years for a second doping conviction. In 2014, Sun served a three-month ban imposed by Chinese authorities after testing positive for a stimulant that was banned at the time. That ban was not announced until after it ended.

Sun's second ban was imposed after a rare CAS hearing held in open court and streamed live online. It lasted more than 10 hours in November 2019 at a special court session in Montreux, Switzerland.

Sun denied wrongdoing.