Several clashes broke-out during and after a Donald Trump rally in Chicago where the Republican presidential candidate was scheduled to speak Friday evening.Trump had arrived at the University of Chicago pavilion ready to speak at the event but was forced to cancel as the crowd of thousands who gathered, including both supporters of the Republican front-runner and those who came to protest his candidacy, grew rowdy.A Trump staffer took the stage nearly a half hour after the rally was slated to begin and told the crowd that the event would be postponed for safety reasons. He did not say when or if it would be rescheduled.After the announcement was made, the crowd began to chant and cheer. Scuffles broke out as signs were ripped from hands and police moved in to break up areas with the most serious conflicts.Cries of "We dumped Trump! We dumped Trump!" rose inside arena where the event was held.An opposing group yelled: "We want Trump! We want Trump!"Outside the pavilion, chants of "We shut it down!" rippled through the crowd on news of the cancellation.Trump decided to postpone the event after arriving in Chicago and meeting with law enforcement, his campaign said.Chicago activists had spent the week leading up to the rally planning how to disrupt it.One group, Showing Up for Racial Justice, coordinated with minority student groups on local campuses, using group email chains and messaging so that protesters could stay in constant communication.One of the organizers, Nathaniel Lewis, 25, a master's degree student in public health at the University of Illinois at Chicago, said he was shocked they succeeded in shutting the rally down."I'm happy, I'm at peace because we came together as a collective," Lewis told Reuters. "This is the last thing we expected to happen, it shows the power of unity."