Around 6:50 p.m. Wednesday, officers responded to 75 Boylston St., where a victim reported being attacked while walking through Boston Common by a group of males and females, police said.

On Thursday, police said there were at least six incidents, but only in four did victims want to press charges. Police and prosecutors offered this summary of the four cases:

Police rushed around downtown Boston Wednesday night, responding to calls for help after a group of up to 20 males and females launched at least six unprovoked attacks on people on Boston Common and in the neighborhood, police said.

About four minutes later, a woman reported that a teenage female started an argument with her while both were walking through the Common. Officers tracked the group that included the assailant to a nearby 7-11 store, where a 15-year-old girl was issued a summons for assault, police said.


In the store, a man identified as Abdirizak Yusef was charged with disturbing the peace when he allegedly became belligerent toward police. The 19-year-old was arraigned Thursday in Boston Municipal Court, where he pleaded not guilty and was released on personal recognizance after a judge declined to revoke his bail on a pending larceny case, Suffolk District Attorney Daniel F. Conley’s office said.

At 8:06 p.m. Wednesday, officers responded to Milk and Devonshire, where a woman reported that she had encountered a group of male and female teenagers, and that a girl in the group had grabbed her purse. When the woman resisted, she was “violently attacked’’ by the girls, police said.

Officers identified a 15-year-old Mattapan girl as the assailant in both the Devonshire Street attack and the first attack on the Common. She was arrested and charged with unarmed robbery and assault and battery with a dangerous weapon, police said.

The last incident occurred at 8:23 p.m. Wednesday when a man reported he was assaulted near Otis and Summer streets and robbed of a bag carrying his cellphone and his iPad.


Jake Wark, the district attorney’s spokesman, said a 15-year-old from Mattapan was arrested in that attack; he also allegedly robbed another man of a cellphone. Also, Wark said, a 15-year-old Mattapan girl was arrested for allegedly assaulting a woman and trying to take her bag in the same area.

The boy and the girl entered not-delinquent pleas to assault and robbery charges Thursday and were ordered held on $10,000 bail and $1,000 bail, respectively, with conditions that they stay away from the alleged victims, Downtown Crossing, and the Common and abide by 6 p.m. curfews.

Advertising copywriter Jack McNamara apparently witnessed one of the attacks.

McNamara said he was walking on Arch Street around 8:30 p.m. Wednesday when he saw about 10 people attacking a man who looked like an office worker from one of the downtown buildings.

“They were really coming down on this one guy,’’ said McNamara. One person, a teenager with short cropped hair and red sweat shirt, was the most aggressive attacker, he said. “I didn’t really realize what was going on until I was in the middle of it.’’

When the victim got up and tried to break away from his attackers, McNamara said, the assailants followed him as he crossed back and forth across Arch Street in search of a safe place to stop. The flow of attackers was “like a swarm,” said McNamara. “It actually enveloped me at one point.’


“It was weird. They would follow him, this whole swarm,’’ he said. “At one point, they just came up to me, but they were totally focused on this guy. I was right there, I could have touched him. [But] I didn’t like the odds at all. I was just standing there motionless.’’

While the teenagers swarmed down Arch Street, McNamara said he saw a male he believed to be part of the group, standing some distance away at the intersection of Arch and Summer streets. This person was watching the violence unfold, while holding closely onto a female McNamara believed was his girlfriend.

Suddenly, the male shouted, McNamara said.

“He just shouted, ‘We out!’ and everyone broke,’’ said McNamara. “They all left.’’

McNamara said that once the swarm flowed past him, he rushed into a nearby 7-11 store, where he called the police.

When officers arrived a minute or two later, he told them what he had seen, as did the victim, who said that he had been subjected to an unprovoked attack and robbed of his cellphone and iPad.

Officer Rachel McGuire, a Boston police spokeswoman, said Thursday that the department does not believe the assaults were part of a “knockout game,’’ which the department considers to be when a person is physically assaulted, but no other crime is committed against them.

McGuire said that at least some of the attacks involved robberies.


Authorities said three people were transported to hospitals after being attacked.

Travis Andersen of theGlobe staff contributed to this report. John R. Ellement can be reached at ellement@

globe.com.

Correction: Because of a reporting error, Jack McNamara was misidentified in an earlier version of this article.