Something troubling is happening to Duboce Triangle. A pleasant, vibrant neighborhood of trees, painted Victorians and parents pushing strollers, it has abruptly taken a turn to violence and drugs.

"There's been a definite shift in the neighborhood," says Eli Blair, who has lived on Church Street for 24 years. "There are times when I am scared to walk my dog. It's not safe."

Residents' worries only increased when a 31-year-old man, Bryan Higgins, was found unconscious at Duboce and Church at 7:30 a.m. Aug. 10. Later in the week, Higgins was taken off life support and died. San Francisco police are investigating the attack as a homicide.

Supervisor Scott Wiener, who represents the district, says the Duboce area "is as bad as I have seen it," adding in a statement that Higgins' death "is another example of the very real public safety challenges we are facing in the Castro/Upper Market area. The problem is extensive, and the vicinity around the Market Street Safeway has real issues."

A cynic could say the problems are just variations of the homeless problem, which has been a part of the fabric of this city for decades. Critics will cue up the "criminalize the homeless" rhetoric and sneer at how this is another case of "gentrification," where new people move in, annex the neighborhood and demand that the undesirables move away.

Except that none of that is true.

The concerned residents aren't newbies to the neighborhood. They are established families.

Nightly incidents

Margaret Garrou has lived there with her husband and their two boys for a decade.

"We moved here in 2004," she said, "and there has definitely been an increase in the past few years. We have had people shooting up on our steps. There's an increase in trash, needles, bottles and used condoms left on the sidewalks and streets. There's something going on every night."

Northern Station police Capt. Greg McEachern says the SFPD is taking the changes seriously.

"These are people who live there, shop there and walk their dogs there," he said. "And they are seeing some activity that is different than what they've seen."

This isn't what we've come to think of as typical homeless behavior - a sleeping bag on the street and some panhandling for spare change.

"I'm not talking about chronic homelessness," said Meredith Brown, who has lived in Duboce Triangle for eight years and has two children who attend public school in the area. "These are really shady characters that you really fear when you are walking down the street. One day I came home from work about 5:30 and there was a guy on the sidewalk, in broad daylight, shooting up.

"My 6-year-old said, 'Why did that guy have a needle in his arm?' "

Repulsive behavior

Some of the incidents are so repulsive that even the most ardent activist would find them indefensible.

Ian McCauley says he has lived in the Triangle for six years with his wife and twin, 5-year-old daughters, who go to kindergarten at a public school in the neighborhood. He says one man took up residence on their front steps and was so persistent that they jokingly referred to him as "the tenant."

"He would be down there all the time," McCauley said. "My wife would come out and see him masturbating."

Thinking that it would help if they cleared out some of the vegetation around the steps, McCauley says they "hit the neighborhood trifecta: a hypodermic needle, a vodka bottle and a crack pipe."

As residents say, the troubling part is that this is new behavior.

Fred Baumer has lived in the area for 19 years.

"The dynamics have changed in the neighborhood," he said, "but there is still no place I would rather live. It's a friendly place where people sit on their steps and parents come by with their kids. People have a sense of stewardship and ownership."

Many of the houses are well-tended Victorians with vivid, colorful trim. Streets are tree-lined and welcoming. Locals walk their dogs up the street to Duboce Park, and there's a nice sprinkling of retail shops and restaurants.

But there are factors that may contribute to the problems. McEachern says there may be some truth to the theory that the Mid-Market revival has pushed bad actors farther up Market Street.

'Some displacement'

"We put a lot of resources in the Mid-Market area," he said, "and we saw some displacement in other places. Not just there, but in lower Polk and lower Hayes Valley."

The recycling center that used to be located in the Safeway parking lot has moved out, but the lot remains a gathering place for marginal types. "The Safeway block is the centerpiece for all that is wrong in the Triangle. It is no-man's land," Baumer says.

There is a hypodermic needle exchange program that sets up once a week on the bike path behind Safeway, and while clean needles are essential to stop the spread of disease, users may toss used needles carelessly. Brown says she's repeatedly found used needles in the park, where there is a children's playground.

And while everyone wants a greater police presence, Wiener says a quirk in the police district boundaries adds a layer of confusion.

"The area is literally at the outer edge of three police districts - Northern, Mission and Park stations," he says. "We're working with all three captains, and they have each been terrific, but they don't have the resources, given the understaffing, to focus at the edge of each of these stations."

Increasing foot patrols

McEachern says: "We are increasing foot patrols to put boots on the ground. "We want people out on the streets to meet the community. That will ramp up when we get more staffing about a month from now."

Good idea, but solutions are tough to come by. There are calls for Safeway to do a better job of managing its property and increased police presence in the troublesome city bike route behind the store. But of all the people I spoke to, only McCauley seemed to have a plan that might work for his family.

"My wife has started to look at real estate listings in Mill Valley," he said.

C.W. Nevius is a San Francisco Chronicle columnist. His columns appear Tuesday, Thursday and Saturday. E-mail: cwnevius@sfchronicle.com Twitter: @cwnevius