The chalk scrawls began showing up in downtown Los Angeles in May.

Members of the Occupy L.A. movement, with the support of some homeless rights advocates, used pastel chalk to express their anger about gentrification in downtown and how, in their view, it was pushing the poor out.

For weeks, the chalk protests were little noticed, and Los Angeles police quietly began arresting the so-called chalkers on vandalism charges.

But on Thursday, a small group of activists gathered at the corner of 5th and Spring streets during the heart of downtown’s popular monthly ArtWalk, handing out chalk to passersby and using the sidewalks as their canvas for more anti-gentrification and some anti-police slogans.

For reasons that are not entirely clear, clashes began between some activists and LAPD officers, resulting in a melee that left four officers injured and more than 15 people arrested. The LAPD called a citywide tactical alert, streamed hundreds of officers into downtown and used less-than-lethal rubber bullets to disperse the crowd.

PHOTOS: Confrontation at downtown L.A. ArtWalk

The incident highlights long-simmering tensions as downtown L.A.'s major revitalization — after decades of decline — has ushered in thousands of new residents as well as upscale lofts, restaurants and galleries to the city core. The gentrification has transformed large swaths of downtown, but it has spread into areas that were traditionally home to some of L.A.'s poorest residents.

Occupy L.A. has made this a central focus as it attempts to rebound since the group’s eviction from City Hall park last year. Both Occupy and Los Angeles Community Action Network, a homeless and low-income advocacy group, have targeted the Central City Assn., the leading downtown business organization, with their protests.

Many of the chalk protests have occurred outside the CCA’s offices on Wilshire Boulevard, which have been hit by nightly encampments as well as loud demonstrations. But it was Thursday’s demonstration at ArtWalk — which is one of the most successful community events of the revitalized downtown — that got the attention.

Cheryl Aichele of Occupy L.A. said her group is concerned that new developments on the edge of skid row are pushing out not only poor residents who can no longer afford rents but also small-business owners. She claims downtown boosters are trying to “criminalize” homelessness by lobbying for more aggressive LAPD sweeps of skid row.

Earlier last month, the Los Angeles Department of Public Works, backed by police and firefighters, had launched a major cleanup effort on skid row, citing the need to address urine, feces, discarded needles and other health dangers listed in a recent county report. The sweep collected nearly 5 tons of trash.

Peter White, co-director of LACAN, said downtown gentrification is another example of the “1%" profiting at the expense of the 99%. “They’ve been lobbying and advocating the 1% and their pretty out-there vision,” he said. “But their vision doesn’t include downtown’s poorest residents.”

On the streets downtown, the dividing line is far less clear. Some residents said they support the right of “chalkers” to protest but don’t fully agree with their take on gentrification. Many were angry that the dispute disrupted their beloved community event.

Patti Berman, a longtime downtown resident and ArtWalk board member, said the activists are on a mission to “de-gentrify” downtown.

“I’m a liberal, I don’t like talking like this,” she said. “But these people have no goals, they just seem to want to cause trouble.... The fact that they wanted to destroy ArtWalk, that’s very hurtful. ArtWalk has done a lot for my neighborhood, and I don’t know what’s going to happen now. I don’t know where it’s going to go.”

Brady Westwater, a longtime downtown resident and activist, was more blunt about Occupy. “It’s a dead movement — it saw its day in the sun — and now they can’t do anything but try and find the place to cause the most disruption at a real community event. Downtown is a real community.”

The debate over downtown’s future has been going on for more than a decade. As its revitalization began, the city made a new push to clean up skid row that included adding more police officers to the streets and cracking down on the notorious drug trade.

CCA President and Chief Executive Carol Schatz said gentrification critics are “attempting to destroy” the growth of downtown.

“LACAN, when push comes to shove, would chase away every one of the residents that has come to live in the empty buildings that were converted to housing,” Schatz said. “They would chase every one of those individuals away, and they would chase every bar and restaurant away.”

She and other downtown advocates said it’s important to look at downtown’s growth in historical context. She said downtown L.A. used to be “dark and empty.”

“Let’s not forget that this revitalization effort has made downtown a vital, thriving place where people are living like they do in Manhattan and Chicago and Philadelphia and San Francisco,” she said. “We brought life to it … we made it a destination.”

Exactly what happened at ArtWalk on Thursday remains the matter of some debate.

Occupy supporters began amassing and chalking at 5th and Spring streets Thursday night.

“They decided they were going to turn ArtWalk into a protest,” LAPD Capt. Horace Frank said. There were a small number of demonstrators, he said, but the crowd grew to 300 as word of the conflict spread. The department set up a skirmish line, and dozens of officers then donned riot helmets and systematically moved the crowd away block by block.

“Our officers then started taking rocks and bottles from the crowd,” he said. “At that point, we fired some less-lethal weapons and eventually gave the order to disperse.”

Frank said chalking is not a protected form of speech, calling it “vandalism.”

Occupy supporters dispute this, adding that the “overdeployment” and “saturation” of police earlier in the evening set the tone for the rest of the confrontations.

“Within 10 minutes of getting to where we wanted to be, there was an arrest,” Aichele said. “It wasn’t even 7:30 yet, and police were using intimidation tactics and pushing us — I got pushed into a garbage can.”

She stressed the group wanted to be peaceful. “In our meeting beforehand, we said our goals were: Have fun. Stay safe. Speak out. Stand up. Reach out. Make friends. Chalk.”

Activists argue that they have the right to hold their “chalk protests” under a 1995 court ruling involving speech rights.

But L.A. Chief Deputy City Atty. William Carter said the state law governing vandalism was changed in 2000 to include the use of any medium, including chalk.

Police had made 12 chalk-related arrests before Thursday’s confrontations, and the city attorney’s office has filed charges in five of those cases. One was deemed an infraction, and four other cases are pending, Carter said. Prosecutors did not file the other cases.

Eugene Volokh, a professor of constitutional law at UCLA, said writing with chalk on the sidewalk is not protected speech and can be restricted by the government.

The question, Volokh said, is “what about hopscotch… I doubt they are going into residential neighborhoods to check.”

rosanna.xia@latimes.com

richard.winton@latimes.com

sam.allen@latimes.com

PHOTOS: Confrontation at downtown L.A. ArtWalk