NEWTON — A small pro-Israel rally turned violent Thursday when a passerby confronted the demonstrators and was shot during a fight with one of the men, authorities said.

The man who was shot sustained life-threatening injuries and was being treated at a hospital, District Attorney Marian T. Ryan said at a news conference.

One of the demonstrators, Scott Hayes, 47, of Framingham, was arrested on charges of assault and battery with a dangerous weapon and violation of a constitutional right causing injury, Ryan said. Hayes has a license to carry a gun, she said.

“This is very early in the investigation,” Ryan said.

The disturbance happened at 6:40 p.m. at the intersection of Washington and Harvard streets, she said.

A small group of pro-Israel demonstrators were on one side of the street, when an individual “apparently completely randomly” walking on the other side of the street, shouted across at the demonstrators, she said.

“Words were exchanged back and forth across the street,” she said.

At some point, the passerby crossed the street and “jumped on one of the demonstrators,” Ryan said.

A “scuffle ensued” and the person was shot by one of the demonstrators, she said.

Hayes is due to be arraigned Friday in Newton District Court.

Acting Police Chief George McMains asked members of the public who may have video of the incident to contact police. He said extra patrols will be added near houses of worship in coming days.

Mayor Ruthanne Fuller described the shooting as a “frightening incident” and asked people to “let the police do their work.”

Newton police and State Police investigators remained at the scene of the shooting for hours. Yellow police crime scene tape cordoned off an area where the fight apparently happened. Yellow evidence markers were visible, along with an Israel flag and a poster.

Kiera McDonald can be reached at kiera.mcdonald@globe.com.