Last year, weeks of protests followed the fatal shooting of unarmed black teenager Michael Brown by a white officer in Ferguson, Missouri, and the chokehold death of Eric Garner in New York City.
About 2,000 people marched on Saturday afternoon through downtown Baltimore, pausing at Camden Yards, home of the Orioles baseball team, where some protesters shouted chants at officers standing guard.
As darkness fell, about 100 protesters splintered from the group and threw bottles, metal barricades and other objects at police officers and their cruisers, authorities said. The windows of several businesses were smashed.
Police arrested 12 people who ignored orders to disperse, authorities said. At least one officer was hurt in the skirmishes.
J.M. Giordano, a photographer who works at City Paper, said police "swarmed over" him and hit him repeatedly. A video of the beating posted to the newspaper's website Sunday shows at least two police officers in riot gear hitting and kicking Giordano as the person filming screams, "He's a photographer! He's press!"
The 41-year-old photographer said his head hit the ground during the beating, which he said only stopped when someone pulled him out of the fray. A spokesperson for the Baltimore Police Department said the incident is under investigation.
Fredericka Gray, Freddie's twin sister, joined Baltimore Mayor Stephanie Rawlings-Blake at a news conference on Saturday where she urged people to keep calm.
"Freddie's father and mother do not want violence, violence does not get justice," she said.
Six Baltimore police officers have been suspended in the Gray case, and an internal police investigation is under way.
Rawlings-Blake, who has called for answers in Gray's death, said agitators at the Saturday protest disrupted the otherwise peaceful political action.
"I am profoundly disappointed to see the violence in our city this evening," she said.
Much of the violence occurred near Camden Yards ballpark, where the Baltimore Orioles played the Boston Red Sox as scheduled. Toward the end of the game, fans were told to stay in place because of safety concerns.
Protesters are calling for the prosecution of the six officers involved in Gray's arrest and a reform of policing tactics. Police have yet to explain when and how Gray was injured.
Melissa Ealey, Gray’s cousin, told Al Jazeera that no crime perpetrated could warrant such abuse.
“There is no reason the police had to conduct themselves in a manner to where…it cost him his life," Ealey said. "I can understand breaking the law is wrong but the way they apprehended him and the things they did where completely against protocol and just inhumane as a whole."
Al Jazeera and Reuters