HONG KONG—A citywide strike and a series of anti-police activities shut down much of what is normally an international financial center and logistics hub here on Monday, as the city entered its ninth week of protests. Cathay Pacific, Hong Kong’s flagship airline, canceled more than 150 flights. The subway was paralyzed. Major banks shut their branches. Shops were closed for the day. The Hang Seng stock index dipped by more than 3.6 percent at market closing, wiping out all gains made since January.

Many of the protesters, who have adopted black as their color and wear it from head to toe, are in their teens or twenties. How did they manage to bring a major city almost to a halt?

“ Empty your mind, be formless, shapeless, like water . . . Water can flow or it can crash. Be water, my friend. ” — Martial arts icon Bruce Lee, "The Dragon"

An organization called the Civil Human Rights Front that is affiliated with all of Hong Kong’s democratic camps, including dozens of political parties and nongovernmental organizations, has pulled together the massive marches that have involved up to two million people at a time. But groups of “front line” protesters have adopted tactics and strategies of their own to express their dissent in ways that resemble guerrilla warfare rather than planned rallies.

The overarching philosophy behind blackshirt actions is “Be Water,” two words lifted from Bruce Lee’s idea of how to overcome what may seem like insurmountable fear: “Empty your mind, be formless, shapeless, like water... Water can flow or it can crash. Be water, my friend.”

Taking the concept even further, protesters have even formulated four principles: “Be strong as ice, be fluid like water, gather like dew, scatter like mist.”

Blackshirts readily admit that their portrayal as heroes fighting for freedom is overblown, and I have more than once heard individuals say, “We’re all afraid. But if that’s why we do nothing, then our future is fucked.” They have taken Bruce Lee’s concept to heart, studying the methods used by civilians in Istanbul, Cairo, and other locales to limit the impact of tear gas and pepper spray.

Some have formed small groups like pit crews, covering canisters with a container like a traffic cone and dousing it with water—to kill the chemical reaction that releases irritant smoke—while using umbrellas to block the views of police cameras that may be aimed at them.

Others have found the perfect implement to extinguish gas canisters by cutting off their oxygen supply—a wok lid, found in any Cantonese kitchen.

Video clips of protests that took place during New York’s Occupy Wall Street and the Arab Spring, at Istanbul’s Gezi Park, and those initiated by Paris’ mouvement des gilets jaunes have found their way into YouTube playlists shared by blackshirts, offering inspiration for countermeasures against the Hong Kong Police Force, or at least visual cues for how a crackdown by security forces may be executed.

Texts like Mao Zedong’s On Guerrilla Warfare, which describes the asymmetric battlefield tactics deployed by the Chinese Communist Party’s militias against Japanese troops in the '30s and ’40s, blend with the idea of “being water” to move dozens, even hundreds, of people from one district to another with unpolished efficiency. Decisions to stop and stage actions are made on the fly, taking into consideration a neighborhood’s geographical layout and exit routes suggested by local residents.

Protesters who have studied Mao’s text realize the irony in referencing the Great Helmsman, as they are, in part, responding to Beijing’s increasingly obvious encroachment in Hong Kong’s governance. But one blackshirt cited Sun Tzu’s The Art of War to me, emphasizing the need to understand one’s enemies, or else face constant defeat and peril.

The syncretic appetite has paid off. By late afternoon on Monday, blackshirts managed to temporarily occupy public areas in at least six districts as well as part of Hong Kong’s airport. Earlier in the day and over the weekend, they also erected makeshift barriers and blocked access to a cross-harbor tunnel that links Hong Kong Island with the Kowloon Peninsula.

In most cases, the presence was meant to be temporary, with retreats to new locations determined by a flow of information about police movements posted on an online forum called LIHKG or communicated via messaging apps.

The idea is to force the police to keep up with mobile groups of protesters who aren’t weighed down by their gear, sapping the security forces’ energy and morale through repetitive motions—and to minimize the number of arrests that are made on any given day. The police have taken 568 people, aged between 13 and 76, into custody since June 9. Among them, 148 were arrested on Monday.

Blackshirts constantly heckle police officers, calling them corrupt, or labeling them as dogs or affiliated with triad gangs. In return, the police berate protesters for being “useless” and call them trash and cockroaches, presumably because they wear dark clothing and scurry in swarms.

The Hong Kong Police Force currently faces massive disapproval and opposition from the public. In just the past few days, they have mistakenly arrested foreign nationals who were not involved with the protests (ignoring explanations made in English), released tear gas that choked the elderly in their homes, forced their way into residential compounds, attacked folks who just happened to be out—even when their commanding officer was issuing orders to retreat.

Yet the police were conspicuously absent whenever groups of armed men in white shirts showed up. On Monday, one crew whacked protesters with bamboo poles; 20 kilometers away, another gang armed with blades and bats was out for blood, slashing and striking people as they charged past.

In an attempt to understand how the police have become a force with their own agenda, decoupled from communities in every district in the city and allegedly willing to collaborate with underworld elements, some blackshirts have sought answers from books like Philip Zimbardo’s The Lucifer Effect and Hannah Arendt’s The Origins of Totalitarianism.

“ Be strong as ice, be fluid like water, gather like dew, scatter like mist. ” — Principles for Hong Kong protestors

On the surface, the protesters of Hong Kong resemble decentralized black bloc groups, with masks and hoods concealing the identities of individuals. But they have refrained from inflicting property damage, which has been a trademark of the blocs in Europe, most recently in Paris. Even during clashes that have taken place in shopping malls, the Hong Kong protesters have been careful, and when they stormed Hong Kong’s legislative headquarters, there were signs put up to remind everyone who entered that books and cultural objects were off limits and had to be preserved, and that theft would not be tolerated.

On Monday, when multiple police stations were surrounded, some being defaced or damaged, a forum post indicated that one particular station is classified as a historic building and heritage site, so protesters backed off.

It is decisions like that one, as well as a general sense of reverence for the cultures that define Hong Kong, that have led to sustained support for the “front line” blackshirts. If the umbrella symbolized the pro-democracy movement that changed the calculus in Hong Kong nearly five years ago, then the hard hat, goggles, and gas mask are objects that have come to exemplify the current tsunami of dissent emanating from all corners of the city—to such an extent that the three items are being sold in packages at some hardware stores, at times nearly at cost.

The blackshirts commit to a wide spectrum of actions, ranging from simple traffic disruptions to more radical responses. For instance, the Chinese national flag has been removed from a landmark pole twice since Saturday and tossed irreverently into the harbor, prompting the city’s previous chief executive to offer a reward of more than $127,000 to anyone who comes forth with information that leads to the prosecution of those involved.

Elsewhere, small groups have hurled bricks and other objects at quarters where the families of police officers reside, drawing criticism. Some used Molotov cocktails last night, chucking them into a police station’s parking lot.

Yet a core tenet of the protests is to leave no one behind, to back each other no matter what, while discouraging tactics that may create volatile situations. So far, that precept holds, and the blackshirts seemed only to have gained additional support from Hongkongers, their loyalty to each other unbroken.

In public spaces, especially on subway trains, information about actions and rallies is not just shared on social media but AirDropped from phone to phone, keeping the citizenry abreast of the latest developments in a direct way.

“ Of course we are fearful. But if that happens, I'm sure every Hongkonger knows how to react, and will be water. We will go back home and sleep. ” — Blackshirt responding to the military threat

Cognizant of the importance of outreach, the blackshirts are taking their message even further, and held their first press conference on Tuesday morning to act as a “counterweight to the government's monopoly” on disseminating information.

Even when facing questions from the press, the overarching philosophy that has come to define every blackshirt action was channeled. Answering a query about how they may respond to intervention by the People’s Liberation Army, one said, “Of course we are fearful. But if that happens, I'm sure every Hongkonger knows how to react, and will be water. We will go back home and sleep.”

In between the musings of a modern kung-fu master, an anti-imperial fighter turned authoritarian, an ancient battle strategist, and contemporary thinkers, the blackshirts’ collective headspace exists. They are the product of a city that refuses to wither away under communist rule. Weekends of rage have become the norm, with flash mob clashes taking place multiple times throughout the rest of the week.

For those in power, winning means a return to the status quo. An agreeable outcome is a more complicated, fractured matter for the blackshirts—and the rest of Hong Kong.

The Chinese Communist Party’s signals have been clear. State-run media outlets released a video of Shenzhen police in drills to handle a situation that resembles what plays out on the streets of Hong Kong. And today, the spokesperson of Beijing’s top office that handles Hong Kong affairs, Yang Guang, warned of the “black hands”—foreign forces—behind the protests, and called upon Hongkongers to defend their homeland. Maybe Yang missed the memo: That’s exactly what they’re doing.