It was unclear what caused police to suspect Lam of rioting on that night
Police have arrested two Hong Kong opposition lawmakers in relation to anti-government protests in July last year, one of whom was suspected of rioting, the Democratic Party said on Wednesday.
Police confirmed Democratic Party lawmaker Lam Cheuk-ting and his colleague Ted Hui were among at least 10 people arrested, without giving further details.
Lam was arrested on suspicion of rioting on July 21, last year, when pro-democracy protests erupted across the Chinese-ruled city, his party's Facebook page said.
During the unrest that day, protesters in the city's downtown area threw black paint at the Hong Kong Liaison Office, China's top representative body, while in the Yuen Long district near the mainland border, a mob of over 100 men wielding sticks and poles attacked pro-democracy protesters and bystanders at the train station.
Lam was hospitalised after being wounded in the face as he livestreamed the attack on his Facebook page.
So far, police have arrested 44 people believed to had taken part in the mob attack, seven of whom have been charged with rioting.
It was unclear what caused police to suspect Lam of rioting on that night.
Lam, along with Hui, was also accused of being involved in a protest on July 6 in the Tuen Mun district, where amid rising anti-Beijing sentiment protesters marched against the "noise pollution" caused by middle-aged women singing and dancing to pop songs in Mandarin, the language spoken in mainland China. Hong Kong people speak mainly Cantonese.
Hong Kong returned to Chinese rule in 1997 under a one country, two systems agreement with its former colonial master Britain that promised it wide-ranging freedoms unavailable on the Communist Party-ruled mainland.
The protests last year were fuelled by perceptions that Beijing was tightening its grip on those freedoms, which authorities have denied.
They began with peaceful marches against a since-withdrawn bill that would have allowed extraditions to mainland China, but clashes between police and protesters became more violent over the following months.
Critics say a new national security law imposed by Beijing on Hong Kong on June 30 has pushed the city onto a more authoritarian path, while its supporters say it will bring stability after a year of unrest.
The law allows for anything China considers to be secessionist, subversive, terrorism or collusion with foreign forces to be punished with up to life in prison.
There have been more protests this year, though far less relentless than they were in the second half of last year.
Restrictions on crowd sizes because of the coronavirus health scare have also helped limit demonstrations.