Lam Cheuk-ting was one of those wounded when a gang of men dressed in white shirts and carrying sticks descended on people -- including those returning from pro-democracy rallies -- at the Yuen Long railway station on July 21, 2019.

The brazen assault, along with criticisms of police inaction, marked a key turning point in Hong Kong's huge and sometimes violent pro-democracy protests at the time, and hammered public trust in the authorities.

Hong Kong has since jailed a handful of those white-clad men, who that night sent some 50 people to hospital, with some perpetrators later identified as government loyalists or as having ties to organised crime.

But in recent years, the government has increasingly chosen to describe the attack as an "evenly matched" fight between opposing sides.

Judge Stanley Chan on Thursday said the incident was the confluence of "two typhoons" and that the seven defendants -- not associated with the white-clad men -- were themselves guilty of rioting.

The seven were present at the railway station during an 18-minute window that was mostly a "standoff" between two camps, shortly before chaos erupted, the judge said.

Lam, who was beaten bloody in the assault, argued at trial that he rushed to the railway station that night to act as mediator and protect members of the public.

But judge Chan said Lam went to the scene to "gain political capital and gather material to attack (political) opponents", adding that his behaviour at the scene had "fanned the flames".

Sentencing for the rioting charge, which carries a maximum penalty of seven years in prison, is set for February 27.

Lam is already behind bars as he was among the 45 Hong Kong opposition figures jailed last month in the city's largest national security trial.

In that case, he was handed a prison term of six years and nine months.