In a video purportedly from the scene first reported by Daily Wire ... you see a man with a mask around his neck shouting at a group of pro-Israel demonstrators, which reportedly included 47-year-old Scott Hayes, an Iraq War veteran.

The unidentified man is heard accosting the demonstrators, whom he called "sick" for "defending genocide" -- before running across the street and physically tackling Hayes.

According to the report, the two men tussled on the sidewalk in Newton, MA -- Hayes then allegedly grabbed his pistol and shot the attacker, who was on top of him at the time.

Bystanders jumped in and began stomping on the man -- and it sounds like Hayes told someone to "grab [his] pistol," and to leave the wounded man alone.

Witnesses said Hayes tended to the man's injuries while waiting for first responders to arrive.

Per Middlesex County District Attorney Marian Ryan, Hayes has been charged with assault and battery with a dangerous weapon and violation of a constitutional right causing injury. However, the D.A. added that Hayes had legal possession of the gun.

Hayes' fellow demonstrators have spoken out in support of him, insisting he acted in self-defense ... though, some said they did not know he had a gun on him.