At least 30 protesters were arrested in the US city of St Louis after a white former policeman was found not guilty of murdering a black suspect while serving in 2011.
Several officers were injured in Friday night's disturbances.
Police say they fired tear gas at protesters who were throwing stones outside the home of the St Louis mayor.
The defendant, Jason Stockley, was cleared of murdering Anthony Lamar Smith, 24, after a car chase.
Mr Stockley, 36, was recorded during the pursuit saying: "Gonna kill this [expletive], don't you know it."
Scuffles began in the afternoon as protesters took to the streets after the verdict.
The home of St Louis Mayor Lyda Krewson suffered considerable damage, police say, as protesters ignored orders to disperse.
Hundreds of people took part in the protest, local TV station KDNL reported. By late evening police declared the gathering an "unlawful assembly".
Agitators are being warned that this is no longer a lawful assembly. If they do not disperse, they will be subject to arrest. #stlverdict— St. Louis, MO Police (@SLMPD) September 16, 2017
As a result of the protests, a concert by the Irish rock band U2 due to take place in St Louis on Saturday night has been cancelled.
The tour organisers say they took decision after police informed them that they were "not in a position to provide the standard protection for our audience".
Mr Smith was a new father and engaged to be married when he was killed on 20 December 2011.
Mr Stockley and his partner said they believed they had observed Mr Smith engaged in a drug deal outside a restaurant.
Police dashcam video and surveillance footage showed Mr Smith reversing his car into the police vehicle twice during his attempt to drive off.
After a three-minute high-speed chase, Mr Stockley told his partner, who was in the driver's seat, to ram Mr Smith's car.
Mr Stockley then ran to Mr Smith's window and fired five shots, hitting him each time.
The former police officer chose to be tried by a judge rather than a jury.
In Friday's ruling, St Louis Circuit Judge Timothy Wilson said the state had failed to prove that the defendant did not act in self-defence.
Prosecutors had accused Mr Stockley of planting a revolver in Mr Smith's car after shooting him. It was recovered afterwards with his DNA on it rather than that of Mr Smith.
Defence lawyers said Mr Stockley had acted in self-defence by killing a drug suspect he believed was reaching for a hidden handgun.
He quit the force in 2013 and now lives in Houston, Texas.
The Board of Police Commissioners settled a wrongful death civil lawsuit in 2013 with Mr Smith's family for $900,000 (£663,000).
Mr Smith's fiancée has urged the community to avoid violence.
Rioting erupted in 2014 in nearby Ferguson, Missouri after the fatal police shooting of an unarmed black teenager, Michael Brown.