According to Press TV, the clashes erupted Friday when Trump campaign managers asked thousands of his supporters at the University of Illinois to leave the arena due to security concerns.
"Mr. Trump just arrived in Chicago and after meeting with law enforcement has determined that for the safety of all of the tens of thousands of people that have gathered in and around the arena, tonight's rally will be postponed to another date," the Trump campaign said in a statement. "Thank you very much for your attendance and please go in peace."
Thousands of angry rally-goers gathered inside and outside the arena and then confronted several hundred anti-Trump protesters, blaming them for the cancellation.
Several fistfights were reported between the two groups before a large contingent of Chicago police officers moved in to restore order.
Supporters of Trump, who were still inside, chanted, "We want Trump" after the event was canceled, while protesters responded by shouting, "We stumped Trump."
Some protesters were being detained and forcefully carried out, according to CNN, which also estimated there were between 8,500 to 10,000 people in the Chicago arena when tensions erupted into chaos.