A realtor who invited clients to tour the neighbourhood for bargain properties and enjoy “artisanal treats” felt the backlash within hours.

“I can’t help but hope that your 60-minute bike ride is a total disaster and that everyone who eats your artisanal treats pukes immediately,” said one message. “Stay outta my fucking hood,” said another.

Fearing violence, the realtor cancelled the event.

An opera company which tried to stage a performance at the park was drowned out by shouts, whistles and a brass band. Students from across town who attempted an educational walking tour of the area encountered masked activists who shadowed them and ordered them to leave.

Welcome to Boyle Heights – or not, depending on how locals view you.

This hardscrabble Latino community, just across the Los Angeles river from the lofts and skyscrapers of downtown, is waging a vigorous and in many ways effective campaign against gentrification.

Where Brooklyn, San Francisco, Oakland and other parts of LA have yielded to and often embraced moneyed outsiders, Boyle Heights has dug a metaphorical moat.

Xochitl Palomera: ‘Our roots run deep here.’ Photograph: Dan Tuffs/The Guardian

An eclectic coalition of residents, business owners, feminists, Maoists and other activists stands guard, working the levers of local government, deploying zoning and legal arguments – and occasionally intimidating perceived interlopers.

The goal is to avoid a flood of money and outsiders which it fears would drive up rents, drive out residents and erase a cradle of Chicano identity.

“Gentrification is a violent threat. When we feel it we may react in an angry way, through fear,” said Xochitl Palomera, an activist with the group Corazón Del Pueblo. “Boyle Heights is not going down without a fight. We know what we’re up against and we’re not afraid. Our roots run deep here.”

Marco Amador, who co-founded a collective space called Espacio 1839, said the battle was not just against gentrification. “It’s about how capitalism works. We’re not just fighting realtors, we’re fighting American capitalism.”

Bold words given that developers are investing billions of dollars a five-minute bike ride away in downtown LA, transforming the skyline with gleaming towers and the streets with boutique bars, restaurants, cafes and galleries.

With rents soaring to Manhattan levels, eyes have turned to the community of 92,000 souls packed into six square miles just across the 6th Street bridge.

Known for low-income housing, mom-and-pop stores, taco stands, service workers and mariachis, Boyle Heights may appear ripe for transformation. Most residents rent, and many are poor. Other Latino enclaves in east LA, after all, have morphed into trendy areas where whites now walk their dogs.

Not so Boyle Heights, at least not yet, as some outsiders have discovered to their cost.

T-Shirts for sale at Espacio 1839 in Boyle Heights: ‘People Yes!, Gentrify No!’ Photograph: Dan Tuffs/The Guardian

Bana Haffar, a realtor with Adaptive Realty in Beverly Boulevard, five miles west, distributed a flyer in May 2014 titled “Why rent downtown when you could own in Boyle Heights?” She invited clients to join her on a bike ride in this “charming, historic, walkable and bikeable neighbourhood”.

Overnight it went viral. Activists organised a protest against the “gentriflyer”.

“I think I was a little naive,” Haffar said last week. “I didn’t know gentrification was such a sensitive topic. Perhaps in retrospect it was not in the best taste. I was pretty shocked at the threatening and violent responses from some people. Some of it was way too much.” Fearing violence, she cancelled the tour.

‘We were all pretty shaken’

Last November Hopscotch, an experimental opera performed in limousines and different locations around downtown, tried to stage a segment in Hollenbeck Park, near Boyle Avenue. Critics had raved about the production, a brainchild of the Industry, LA’s premier avant garde opera company.

Protesters in Hollenbeck Park felt otherwise and barracked the performers. “I made efforts to speak to a woman who appeared to be in charge but was always ignored and often shouted over,” recalled Marc Lowenstein, the company’s music director. “Some of the things she said were: ‘This park is for brown people’ and ‘This is not a park for white people. You are white people.’”

A march in support of the 20th-century Mexican revolutionary Emiliano Zapata on 10 April in Boyle Heights. Photograph: Dan Tuffs/The Guardian

Things escalated on the show’s final day when members of the Roosevelt high school band used saxophones, trombones and trumpets to drown out the opera. Performers moved to another side of the bandshell but the high school band followed them, urged on, according to Lowenstein, by activists from a group called Serve the People LA (STPLA).

“I asked our own musicians to play along with the high school players, to engage them. The Serve the People members, though, encouraged the high school players to become physically intimidating and they themselves became physically intimidating.”

The opera fled. “We were all pretty shaken by two things: one, the physical intimidation, and secondly, the use and manipulation of the schoolchildren,” said Lowenstein.

In December, a few weeks later, a group of students, artists and young professionals from across the river attempted a walking tour focused around the historic 6th Street bridge, which was due to be demolished and rebuilt.

“None of us were property owners or had any interest in buying property,” said Karl Baumann, a PhD student who helped organise the tour. He is no fan of gentrification, calling it a beige wave that erases difference and flattens culture. “It’s like this reversal of race-based housing covenants and nimby policies in rich white areas.”

A skate boarders at Hollenbeck Park, where an opera performance was disrupted by local campaigners. Photograph: Dan Tuffs/The Guardian

Even so, STPLA activists with bandannas ordered Baumann’s group to leave. Feeling misunderstood, it complied. “I wouldn’t use those tactics,” said Baumann. “But as an outsider I can’t tell them what does or doesn’t make sense for their community. They assume the worst unless proven otherwise.”

The STPLA is an offshoot of the Red Guards, Los Angeles, which aims to build a communist Maoist party and deliver “complete liberation from the capitalist state”.

It formed in April 2015 and has sister groups in Austin, Portland and Washington DC, said a spokesman, Alex Brownson, 25. Confronting uninvited outsiders was part of a strategy to rebuff an “onslaught of development”, he said.

“Our emphasis is not on hipsters and white people walking our neighbourhood but when they come here … perhaps these folks should feel uncomfortable. Boyle Heights is not a poverty zoo for wealthy people from west LA.”

Brownson said the opera alienated locals because performers were mostly white and sang in English, not Spanish. The schoolchildren’s musical bombardment was spontaneous and not orchestrated by STPLA members, who were there to distribute food and clothes, he added.

The STPLA planned to support a new group called Defend Boyle Heights which had recently formed, said Brownson. “Their work has yet to be seen.”

Mynor Godoy: ‘People are in desperation mode.’ Photograph: Dan Tuffs/The Guardian

Another member, a 27-year-old Mexico-born pest controller who identified himself only as Beto, vowed further actions. “We won’t sit by and let Boyle Heights be taken over.”

The militants appear few in number – possibly just a handful – but have backing from other groups who work through official channels.

“Gentrification in Los Angeles has occurred clockwise, progressing from Silver Lake to Echo Park to Eagle Rock to Highland Park to Lincoln Heights and now Boyle Heights. As a neighbourhood, we have seen how quickly communities in Los Angeles can change,” said Steven Almazan, outreach chair of the Boyle Heights neighbourhood council.

The protests sent a message to outside organisations and developers, he said: “If you are going to exploit or disrupt our community, we are going to defend our community.”

Mynor Godoy, the council’s chair of planning and land use, said that after enduring decades of official neglect residents bristled at the prospect of displacement. “It has built up to point where people are in desperation mode and no longer know where to go.”

Rebellion is in the area’s DNA. Yiddish-speaking Jewish immigrants with liberal, socialist and communist ideals stamped their identity here before the second world war. Mexican immigrants who followed helped forge the Chicano civil rights movement in the 1960s, a heritage emblazoned in murals around Mariachi Plaza. Posters of Bernie Sanders as Pancho Villa adorn some store windows.

Bernie Pancho Sanders in Boyle Heights gallery window. #FeelTheBern pic.twitter.com/YMqGJSVSxA — Rory Carroll (@rorycarroll72) April 13, 2016

Community groups who carried on that spirit could not stop city authorities sandwiching the neighbourhood between freeways, or skimping on green spaces, but together they try to bolster community cohesion, resist gentrification and shape public policy.

They range from the East LA Community Corporation, which engages local government and state agencies, cultural advocates like Espacio 1839 and Corazon del Pueblo and feminist groups like the Ovarian Psycos Bicycle Brigade. The return of college-educated, upwardly mobile Latinos – a process dubbed “gentefication” after the Spanish word “gente”, which means people – has bolstered the community’s lobbying clout.

Is gentrification inevitable?

Activists scored a victory last year when the Metropolitan Transit Authority scrapped a proposed $49m shopping complex over concerns it would be sterile, dent local retailers and displace traditional musicians who congregate at Mariachi Plaza. Once a venue for drug gangs, it has become cleaner and safer without losing its identity.

Despite the resistance some gentrification appears under way. Galleries fleeing high rents in the arts district have leaped across the river. Laundromats and a venerable dive bar, Las Palomas, have closed. Posters offering to buy homes for cash sprout from lamp-posts. Property values are surging.

“A year ago a fourplex would have gone for approx $500,000. Now you’d see it on the market for $800,000 and above,” said Haffar, the realtor. Is gentrification inevitable? “That’s what it looks like.”

Roberto Olmos sits with his friends playing music in Mariachi Plaza. Photograph: Dan Tuffs/The Guardian

Much depends on the wider economy and property market. If the moat is breached, not everyone dreads the prospect. “Longtime property owners see great potential in redevelopment and gentrification,” said Michelle Levander, co-editor and publisher of Boyle Heights Beat. Cafes and stores, for instance, – those that survived rent increases – would gain extra customers.

Seated in Mariachi Plaza, Roberto Olmos, 69, a mariachi, felt torn about gentrification. It might bring improvements but also drive up his rent and banish him from Boyle Heights. “Make it all shiny, great. But then what? The gringos will come.”