Authorities say a police officer in Wisconsin shot and killed a black teenager after a struggle Friday night, prompting a protest from a small group of demonstrators.

Madison Police Chief Mike Koval said police responded to a report of a man jumping into traffic around 6:30 p.m. An officer then went to an apartment where the man had gone and entered after he heard a disturbance inside.

The Wisconsin State Journal reported police did not reveal the victim’s name, but family and friends identified him as Tony Robinson, a 2014 high school graduate.

Koval said the officer shot Robinson after the teen assaulted the officer. The police chief did not know if Robinson was armed but said the “initial findings at the scene did not reflect a gun or anything of that nature that would have been used by the subject.”

After the shooting, a crowd of demonstrators from the Young, Gifted and Black Coalition gathered at the scene of the shooting and started chanting “Black lives matter,” a refrain used in protests last year regarding the Michael Brown shooting in Ferguson, Mo. and the chokehold death of a black man by a New York City police officer.

Robinson’s grandmother Sharon Irwin told the paper the teen was unarmed and posed the question to police, “What happened to your Taser?”

The paper said it was unclear how she knew her grandson did not have a weapon.

She urged protestors to be peaceful. “I think you need to rise up but I don’t want violence,” she said.

WKOW-TV interviewed Robinson’s mother who said her son would not harm anyone.

“My son has never been a violent person,” she said. “And to die such a violent, violent way, it baffles me.”

Koval said more than one shot was fired during the incident. He said there was a second call reporting that the man jumping in traffic was "responsible for a battery."

“In light of so much things that have happened not just across the country, but in our own community, it’s understandable that the reaction at the scene and of some our citizens is extremely volatile, emotional and upsetting," the police chief said, according to WKOW. “And we understand that. That’s absolutely appropriate under these circumstances.

He also urged protestors to exercise restraint and let the investigation of the shooting take its course.

That investigation will be conducted by the Wisconsin Department of Justice’s Division of Criminal Investigation.

Madison Mayor Paul Soglin called the shooting “a tragedy beyond description.”

He said because of the state-required outside investigation, Madison police will be able to offer only few details.

The Associated Press contributed to this report.