Defence counsel Fiona Nam said there was not a day her client “hasn’t looked back in regret” at the events that led to his arrest.

In a letter to the court, Sin wrote: “If I had a chance to talk to young people, I would urge them not to resort to violence.”

The District Court heard he was among thousands of protesters who surrounded the Legislative Council Complex when the legislature was supposed to resume the second reading of the controversial Fugitive Offenders Bill.

If passed, the legislation would have allowed Hong Kong to send suspects on a case-by-case basis to jurisdictions it did not have an extradition agreement with, including mainland China and Taiwan.

Officials have called this protest a riot. But that categorisation quickly became one of the contentious points fuelling what would become months of anti-government demonstrations, with protesters naming the retraction of that label as one of their five demands.

A week after Chief Executive Carrie Lam Cheng Yuet-ngor met another one of the five demands to withdraw the bill on September 4, Sin was charged with one count of rioting and two of resisting a police officer.

As it happened: Hong Kong police and protesters renew clashes as tear gas flies

On Monday, he pleaded guilty to the rioting charge, which is punishable by a maximum of 10 years in prison, but capped at seven years at the District Court.

He denied two other charges, alleging he resisted two unnamed officers on the same day. These two counts were kept on court file, meaning they cannot be pursued without the order of this court or the Court of Appeal.

Acting senior public prosecutor Karen Ng Ka-yuet said the rally organised by Civil Human Rights Front and attended by some 8,000 to 10,000 protesters initially began as an authorised protest, but it escalated into a riot when protesters persistently charged police cordons and hurled objects at officers.

Eight officers were injured during the riot and 39 people were arrested over the events on the entire day.

The court heard Sin stood at the forefront of the crowd and did not retreat even after tear gas was fired. He was subdued and arrested at the scene after two officers saw him pick up an unknown object from the floor and hurl it at police.

In terms of sentencing, Ng said the court could consider the case of localist leader Edward Leung Tin-kei, who was jailed for six years on a single count of riot over the Mong Kok unrest on Lunar New Year in 2016, or that of Yeung Ka-lun, who was given 57 months on the same charge plus arson for setting a taxi on fire that night.

Nam accepted that public order was breached on the day and her client’s actions were violent.

But she said such conduct was “completely out of character” for her client, whom family, friends and colleagues had described as an honest, kind-hearted, loving, polite and responsible young man.

“He had dreams about his future,” Nam said. “He was arrested and his life was forever changed. His family was astonished … There has never been a day he hasn’t looked back in regret.”

Nam said her client owed an apology to those who loved him, as well as to those who shared the same beliefs because he had set a bad example by resorting to violence when he was “caught by an outburst of emotions” in a heated confrontation with police.

But the counsel also noted his involvement in the riot was spontaneous and limited to three to five minutes.

He had no intention to cause damage or physical harm, and there was no evidence he had brought the items he hurled at police to the scene, she added.

“I submit this case is not the most serious in the spectrum of cases,” Nam said. “You have a young man before you who is extremely remorseful.”

The defendant had no prior convictions. District judge Amanda Woodcock will sentence Sin on May 15.