A mostly peaceful demonstration that began at Grant Park's Petrillo band shell ended with a violent clash at 22nd and Michigan Avenue just outside McCormick Place on Sunday.
A number of Black Bloc protesters in the crowd pushed toward a police who'd formed a barrier in front of barricades. Police Supt. Garry McCarthy stood just behind the line of police giving orders.
Officers scuffled with aggressive protesters who could be seen tossing clubs and pushing police. Police pushed back and occasionally used force to push back protesters.
Authorities commanded the group to disperse.
Chicago police officers began removing some of the more aggressive demonstrators from the crowd in a method known as extraction.
Some protesters appeared to suffer injuries. One man was seen bleeding from his eye; another woman was being doused with water after collapsing on the ground. McCarthy later said four officers were injured.
During the scuffle, some protesters disassembled metal barricades and tried to use them as weapons against the police.
After about an hour, police gave a warning to disperse before bringing out a Long Range Audio Device, or sound cannon, which is used to sound loud, clear messages. It can also emits a powerful, focused audio wave that can cause damage to the ear. It was only used Sunday to send messages.
Officers were also seen putting gas masks on themselves and some horses, but tear gas was not released.
By 6:30, police seemed to have control of the intersection and had pushed the protesters westward.