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Hundreds of protesters descended on the home of a Los Angeles police officer Wednesday after video surfaced of the off-duty cop's apparently firing a gun during a scuffle with a 13-year-old that erupted after the teenager and friends allegedly walked on his lawn.

The teenager wasn't hit by gunfire, but Jennifer Dorscht, his grandmother, told NBC News that he sustained "a lot of bruises" during Tuesday's altercation in Anaheim, 25 miles southeast of Los Angeles. No one else was injured.

Twenty-four protesters — 10 men, eight women and six juveniles — were arrested near the officer's house, and there were reports of windows broken and other acts of vandalism, Anaheim police said in a statement Thursday.

Sgt. Daron Wyatt, an Anaheim police spokesman, told NBC Los Angeles that the officer has been in an "ongoing dispute" with "a number of juveniles who continually walk across his property."

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"He's asked them to stay off the property," but on Tuesday, "it happened again, and it led to a verbal confrontation between the off-duty officer and a group of individuals," Wyatt said.

Wyatt said statements indicated that the officer was "trying to detain the individual until the Anaheim PD could arrive based on an alleged threat that the 13-year-old was going to shoot the off-duty officer."

The officer wasn't arrested because "there was no ongoing threat to public safety," Wyatt said. "We know how to find him, where to find him."

The video, which was shared widely online, appears to show the officer holding on to the 13-year-old boy while being jostled by the teen's friends. The tussle continues until the cop pulls the pair into a hedge before pulling out his weapon and firing it. It doesn't show how the confrontation began or what led to the incident.

"My understanding from the statements was that the round was not fired at anyone, was not even fired in the direction of the individuals involved, but may have been more towards the ground," Wyatt said.

Protesters march toward the off-duty Los Angeles police officer's home late Wednesday. Joshua Sudock / AP

But Anaheim Mayor Tom Tait said in a statement that "like many in the community, I've seen the video and I'm very concerned about what it shows."

"Anaheim is committed to a full and impartial investigation," Tait said. "Our city will move forward without delay."

Los Angeles police have also launched an internal investigation into the officer's actions. They said the confrontation "began over ongoing issues with juveniles walking across the officer's property."

The Los Angeles Police Department didn't identify the officer, who is on administrative leave. The 13-year-old was arrested and released after being booked at Orange County Juvenile Hall on charges of criminal threats and battery. A 15-year-old friend who was arrested on suspicion of assault and battery was released to his parents.

Dorscht, 45, said her grandson was sticking up for a 13-year-old girl who drew the officer's ire. She said the officer swore at the kids.

"It's just a terrible situation," she said at Children's Hospital of Orange County, where the boy was examined. "It could've been handled completely in a different manner. He's a good kid. He does all the right things. He has a good heart. I think that's why he stuck up for this girl."

Protesters gathered outside the off-duty LAPD officer's home in Anaheim. Joshua Sudock / AP

Jennifer Rojas, a policy advocate at the American Civil Liberties Union of Southern California, told NBC Los Angeles that the organization was "deeply disturbed" by the reports and had demanded "a full explanation of why, in an altercation between the police officer and youths, the youths were arrested but not the officer who fired his gun."

"An officer, even off duty, has an obligation to follow the law and protect public safety, rather than threaten it," Rojas said. "The LAPD officer's actions on the video are grossly irresponsible."