HONG KONG (NYTIMES) - When protesters in Hong Kong last weekend came upon an older, shirtless man who was threatening a crowd, they pounded him to the ground with a stick. When a taxi swerved into a group of protesters nearby, some dragged the driver out and beat him until he was covered in blood.
And a few blocks away, protesters punched Hong Kong actress Celine Ma who has publicly supported the police - apparently because she had been taking photos of protesters who were vandalising a bank.
"Go back to the mainland!" the protesters yelled as she left the scene.
A confrontational core of Hong Kong's anti-government protesters have acted with greater ferocity in recent weeks, attacking individuals and smashing and torching storefronts, banks, cafes and subway entrances. In a strikingly personal affront, one group even delivered a severed pig's head to a police officer's wedding banquet.
For months, the protests, which began out of anger towards a proposed extradition law but broadened to encompass a variety of demands, have been largely peaceful. However, violence now regularly overshadows events.
The hardline protesters see themselves as being forced to mete out justice in a system that lacks accountability and in the face of a government they deem unresponsive. Much of the violence has been fuelled by anger over police conduct, made worse after an officer shot and wounded a teenage protester with a live round during clashes on Oct 1, the politically sensitive anniversary of the founding of the People's Republic of China.
But to their critics, these protesters are crossing the line by playing the role of vigilantes to punish those they consider their foes. The intensity of the unrest could alienate moderate supporters and members of the public, and play to Beijing's depictions of the movement as the work of riotous mobs.
"Some people began to take matters into their own hands," said academic Ma Ngok, an associate professor of government at the Chinese University of Hong Kong. He pointed in part to the protesters' frustration that the police have failed to arrest and prosecute pro-government thugs who attacked demonstrators.
Yet, he added, in recent days, the movement has been debating whether such retributive violence is morally justifiable.
The protesters describe vigilante attacks as "settling matters privately", or "si liu" in Cantonese. On Internet forums where rallies and gatherings are organised, some posts calling on protesters to return punches have gained traction on the ground.
In their effort to retaliate against perceived injustices, hardline protesters see few actions that are off-limits.
A group of them showed up last month at a hall where an off-duty police officer was holding a wedding banquet and delivered a severed pig's head. They also set off an ear-piercing fire alarm and tossed fake money at guests, turning a Chinese funeral custom into a deep insult.
One of the protesters who was there, Mr Edward Hui, 20, said that the harassment is justified because police are getting away with what protesters see as excessive brutality.
"This sends a message to the police that, even if they are not held accountable by the system, they will be punished in their daily lives, and their loved ones too," he said.
The decision by Hong Kong's leader, Mrs Carrie Lam, to invoke emergency powers last Friday (Oct 4) to ban the use of face masks at protests has only further angered the protesters, who see it as the latest example of eroding freedoms in the Special Administrative Region.
Many who attended rallies on Sunday wore masks in defiance of the ban.
In the Mong Kok neighbourhood on Sunday night, two men in masks who looked to be in their 20s or 30s punched a shirtless, older man who was standing in the street and arguing with a crowd.
The man tried to walk away after being hit at least three times - in the face, neck and jaw. But another masked attacker struck him on the back of the head with a stick, knocking him to the ground, and hit the man again.
In another confrontation, video footage circulating online showed a group of protesters pulling a taxi driver out of his car and beating him bloody after his vehicle accelerated with a sharp swerve into a crowd.
Some protesters formed a circle around the driver in an apparent effort to protect him, but by then he was already bleeding profusely from his head. At least one protester was reportedly injured by the swerving car.
"Rioters blatantly launched brutal attacks on ordinary citizens yesterday," the police said in a statement on Monday, referring to the beating of the taxi driver and other confrontations that day. "Such acts of violence by far overstep the moral boundaries of any civilised society."
Protesters have also begun setting more and more street blazes, which send plumes of black smoke swirling through Hong Kong's urban canyons. Fires at the entrances to metro stations have been set to show anger at the transportation network's perceived support for the government. The fires have added a sharp edge to a slogan from the "Hunger Games" movies - "If we burn, you burn with us" - that the movement appropriated months ago as a challenge to the city's political elite.
Many protesters and organisers have avoided overtly criticising violence on the part of the demonstrators, asserting that any fracture in their unified position weakens their influence. But there were signs that more demonstrators were concerned that the escalation in violent tactics, even if justified to many, would undermine the movement.
On Sunday, a post on the Reddit-like forum LIHKG, used by protesters, urged demonstrators to resist the incitement to violence. The post, which was upvoted more than 1,800 times, asserted a theory that Internet commentators paid by the Chinese government could be pushing protesters to adopt extreme tactics to try to sow divisions within the movement and erode public support for it.
Another popular post in the early hours of Monday suggested that the protesters should dial down the use of violent tactics and stop their acts of vandalism. That post was also heavily endorsed.
But there are signs that the public might be growing more tolerant of violence.
The Chinese University of Hong Kong conducted a survey of more than 600 people that found that the proportion of people who believe that protesters should uphold the principle of non-violence had fallen to 70 per cent in early September, from 83 per cent the month before. More than half of the respondents said that they could understand the use of extreme tactics by protesters when the government is seen as having failed to respond to public demands.
Mr Wong Siu Fan, a 25-year-old logistics worker who has participated in several peaceful protests, said he believed the hardline protesters were usually justified in turning to violence, but he was worried about its escalating frequency.
"It could make a lot of people feel that the protesters' goal is no longer to resist the government, but to vent," he said. "I'm not optimistic because the government is pushing protesters to extremes, and then afterwards using their actions to stigmatise them."