Police in San Francisco's East Bay are meeting on Friday to address what they say is a phenomenon called "wildings," where packs of teens gather in public places and create mayhem in their wake.



The meeting was prompted most recently by "wildings" terrorizing San Leandro. Authorities say that over the last few months, large groups of teenagers - as many as 100 - have been attacking, scaring and robbing victims at malls and at near BART stations. On Friday, the police department put out a flyer about this"new crime trend" involving "unruly young adults."



The term "wilding" was first dubbed after a cruel attack in New York's Central Park in 1989, when a female jogger was attacked, raped and left for dead.

The name stuck and authorities say the trend of "flash mob crime sprees" has now spread across the United States and beyond. According to the Urban Dictionary, the slang term refers to "marauding in bands to terrorize strangers and to swagger and bully."

Sometimes the wilding groups post on Facebook and Twitter to arrange meetings, according to reports of incidents. And many "wildings" have been captured and posted on YouTube, from Philadelphia to Chicago. In late May 2013, more than two dozen teens were arrested after mobs began arresting pedestrian's on Chicago's Magnificent Mile.



In March, teens in Washington, D.C., hit a high-end jeans store in what police called a "flash mob" robbery.

In 2008, teenagers in St. Louis began attacking riders at train stations, according to GateAmerica, a blog for law enforcement and prevention specialists.

"These acts began to snowball through Boston, South Orange, N.J. and Brooklyn. Milwaukee had an a group of 50-60 teens disrupting a area Shopping Mall in January of 2011. Now it has infected Chicago," the GateAmerica blog says. "Thus flurry of attacks included 8 attacks in just one weekend and the closing of one of the most famous beach's in the Midwest, North Avenue Beach."



According to San Leandro Police Lt. Rick DeCosta, three attacks occurred within the last week, and two teens have been arrested. The attacks include:



May 31: Two juveniles at the Bayfair BART station were confronted by a large group of 10- to 20-year-olds about 10 p.m. Police said someone in the group challenged the minors to a fight and one of the suspects threw a punch, prompting the kids to run away. Police said the juveniles got separated during the chase and the suspects caught up to one of them at the Bayfair Mall parking lot, knocked him to the ground and kicked and punched him before taking his cellphone and Nike tennis shoes. No one was arrested.

Two juveniles at the Bayfair BART station were confronted by a large group of 10- to 20-year-olds about 10 p.m. Police said someone in the group challenged the minors to a fight and one of the suspects threw a punch, prompting the kids to run away. Police said the juveniles got separated during the chase and the suspects caught up to one of them at the Bayfair Mall parking lot, knocked him to the ground and kicked and punched him before taking his cellphone and Nike tennis shoes. No one was arrested. June 2 : Two middle school students were walking in the 2100 block of East 14th Street about 4 p.m. when three teenagers approached the boys and tried to take a shopping bag with expensive Nike shoes that one of the boys was carrying, police said. When the boy resisted, one of the suspects pulled out a handgun and pistol-whipped him, knocking him unconscious. The boy who was struck with the gun was taken to a hospital and received several stitches.

: Two middle school students were walking in the 2100 block of East 14th Street about 4 p.m. when three teenagers approached the boys and tried to take a shopping bag with expensive Nike shoes that one of the boys was carrying, police said. When the boy resisted, one of the suspects pulled out a handgun and pistol-whipped him, knocking him unconscious. The boy who was struck with the gun was taken to a hospital and received several stitches. June 2: Police said there was another robbery about 4:40 p.m. in a parking lot two blocks north on East 14th Street. Witnesses told investigators the victims, who had a 2-year-old child in their vehicle, tried to pull into the parking lot but were blocked by several teens at the entrance. Police said the victims asked the teenagers to move, but several starting yelling obscenities at them. Police said the adults got out of the car, leaving the child inside, and confronted the teens. At that point, police said one teen began ransacking the passenger side of the car, stealing several items. Police said another teen then got into the driver's seat, put the car in gear and started to drive away with the child still inside. The victims pleaded with the teenager to stop and eventually, the teen pulled the car over. Police said the suspects stole a computer tablet and an iPhone. Two teens in this case were arrested on charges of asault with a deadly weapon, carjacking, kidnapping and child endangerment.



NBC Bay Area's Mark Matthews and Bay City News contributed to this report.