The doping control assistant (DCA) lacked proper accreditation and took photos of Sun without his permission, leading him to refuse the blood sample collection.

[6] However, on 28 February 2020, the Court of Arbitration for Sport (CAS) overturned FINA's decision, banning Sun for eight years for tampering with the doping control process.

Some analysts opined that the trial was marred by severe translation problems, conflict of interest, bias and an "absence of evidence" around doping activity.

[25] On the first day of competition at the 2011 World Championships in Shanghai, Sun came 2nd in the 400 metre freestyle with a time of 3:43.24, 1.2 seconds behind South Korean Park Tae-hwan.

At the initial line-up on the starting blocks, a step-down command was issued because of noise from the crowd, but instead of stepping back, Sun reacted by diving in.

The officials ruled the early dive was the result of noise from the crowd and did not constitute a false start, and Sun was allowed to continue in the competition.

[40] This result made Sun the second swimmer in history, after Grant Hackett, to win gold medals in all three long-distance freestyle events—400, 800, and 1500 metre—in a single World Championships.

Aiming to become the first man to win seven gold medals at a single championship, he added to his range the 100 metre freestyle, an event typically reserved for sprinters.

[43] In May 2014, the Chinese Swimming Association handed Sun a warning but let him off without suspension after he tested positive for trimetazidine, a drug that was banned four months earlier and classified as a stimulant at the time by the World Anti-Doping Agency (WADA).

The lenient penalty was based on this: Sun said that Dr. Ba Zhen, an Olympic team doctor for Chinese swimming, prescribed the drug to treat heart palpitations, a condition he has suffered since 2008, and was unaware that it had been newly added to the banned substances list.

Ba Zhen also played a part in events that led to Sun's suspension for four years and three months after an altercation with anti-doping testers in September 2018.

[53] Sun also participated in the 4 × 100 metre freestyle relay, helping China win gold with an overall time of 3:13.17, setting a new Asian Record in the event.

[62] FINA executive director Cornel Marculescu explained that the altercation that led to a complaint against Sun was due to congestion in the warm-up pool, and did not warrant further action.

Horton's social media pages garnered negative criticism from Chinese fans, with many calling the Australian as a racist, a "snake", and a "disrespectful person".

[87][88][89] In December at the 2018 FINA World Swimming Championships (25 m), Sun participated in the 4 × 200 metre freestyle relay, helping China win bronze.

[91][92] In the 400 metre freestyle, Sun won gold with a time of 3:42.44, finishing 0.73 seconds ahead of runner-up Horton and earning his fourth consecutive title in this event.

[96][6] At the 2024 National Summer Swimming Championships in Hefei, Anhui, Sun Yang got the second place with a time of 3:54.98 in the preliminaries, which is the first appearance after a 51-month suspension.

[46] Sun was tested while competing in the Chinese national swimming championships, and said that a doctor prescribed the drug to treat heart palpitations, a condition he has suffered since 2008, and that he was unaware that it had been newly added to the banned substances list.

[100] The World Anti-Doping Agency (WADA) admonished the Chinese Swimming Association for tardiness in reporting the failed test and the subsequent ban until after it had been served, meaning that Sun never missed a major event.

[46] CHINADA (China Anti-Doping Agency) deputy director Zhao Jia said that "Sun proved with sufficient evidence that he did not intend to cheat, which helped reduce his ban to three months", but he was stripped of his win in the 1500 metre freestyle at the 2014 Chinese nationals.

WADA disagreed with FINA's decision and appealed to the Court of Arbitration for Sport (CAS), which accepted the case and held a public hearing in November 2019.

[121] In January 2019, The Sunday Times published an exclusive article reporting that Sun and his entourage had presided over the smashing of a vial of the swimmer's blood sample with a hammer in front of anti-doping testers and that he may face a lifetime ban.

[123] After The Sunday Times report, Wada, the global anti-doping regulator opened an inquiry and announced on March 13, 2019, to appeal the ruling at the Court of Arbitration for Sport.

[124] CAS issued a report on 20 August 2019, stating the appeal hearing brought by WADA against Sun and FINA in September had been postponed due to a party's unexpected personal circumstances.

[112][135][136] WADA's lead counsel Richard Young referred to "concerns over intimidation and protection issues", while during cross-examination of witnesses WADA co-counsel Brent Rychener highlighted the threats and warnings made by members of Sun's entourage to the testing officers, including exchanges involving the swimmer's mother, Dr. Ba Zhen (the head of the Chinese Swimming Association), and Dr. Han Zhaoqi (the head of the Zheijang Anti-Doping Center).

At no point ... did he confront the possibility that he might have overreacted in his actions.“ [10][138]WADA issued a statement welcoming the verdict, saying that the "CAS ruling confirms those concerns" about the original FINA decision that seemed to be incorrect under the World Anti-Doping Code.

[150] The CAS decision against Sun Yang was scrutinized, and many unknown facts about the case were brought to light, in an article[151] published at Sports Integrity Initiative in 15 May 2020.

The article stated that CAS decision against Sun Yang was "unfair" and needs to be overturned given the extenuating circumstances such as the test team not meeting standards and that the "DCO failed to give the required warning".

[152][118] The South China Morning Post identified one of Frattini's tweets as "describing one person who appeared to mistreat a dog as a 'yellow face Chinese monster'".

"[178] On 6 November, the State General Administration of Sports announced that Sun was temporarily banned from the national team swimming camp and all competitions and business-related activities.