Aamer Madhani and Steph Solis

USA TODAY

CHICAGO — Donald Trump, the GOP presidential front-runner, postponed his rally Friday night over security concerns after protesters and supporters clashed at the University of Illinois at Chicago.

Chaos ensued after organizers announced the rally was canceled shortly after 6:30 p.m. at the UIC Pavillion. Police ejected at least a half dozen anti-Trump demonstrators, including one man who snuck on stage and approached the podium.

Chants of "Trump" and "Bernie" alike filled the arena as police dispersed the masses.

Joe Fritz, 20, who came to hear Trump speak, said a woman punched him as he stood in a crowd of protesters outside the arena after the rally was canceled.

Fritz said the woman landed a glancing blow to his chin after he questioned her for yelling epithets toward cops standing nearby and about Trump. Fritz said the woman was with a girl who was about 10.

"I told her, 'What kind of example are you setting?'" Fritz said.

Fritz said he and his friend were then surrounded by other anti-Trump protesters who screamed at them before police pulled them out of the crowd.

Still, the scuffles were brief, and some protesters said the security concerns were overstated.

"(Trump) felt us tonight and felt our power tonight," said Angelica Salazar, 30, of West Chicago, Ill. Salazar, who went to speak out against Trump's anti-immigrant rhetoric, said she did not feel unsafe.

Trump cancels Cincinnati rally

Matthew Ross, a Chicago activist, said suggestions from Trump that protesters presented a security risk don't hold up.

"Have you seen what his supporters have incited at their rallies?" said Ross, who said he had water thrown at him by Trump supporter after it was announced that the rally was canceled. " I think what he (Trump) is doing is inciting violence."

The Chicago Police Department said late Friday that four men and a woman were arrested at the rally. Police officials did not detail charges or release names of the individuals taken into custody.However, CBS News said its reporter, Sopan Deb, was detained by law enforcement while covering the scene.

CBS reporter detained while covering Trump rally, protest

Anthony Guglielmi, a police department spokesman, said the Trump campaign did not consult the police department before canceling.

"They did not consult us at all," he said. "The decision was made by the campaign on its own."

While many dispersed after the rally was canceled, hundreds of people protested outside. They chanted and cheered, as supporters screamed back "Trump! Trump! Trump!"

Trump never made it there, citing security concerns in interviews with multiple news networks. He described anti-Trump protesters, including those at previous rallies, as violent.

"I just don't want people hurt," he told MSNBC.

Trump has faced criticism about violent comments he and his supporters have made on the campaign trail. When attendees at an event in November kicked a Black Lives Matter activist, Trump said, "Maybe he should have been roughed up," according to The Washington Post. Another supporter, John McGraw, sucker-punched a protester at a rally Wednesday in North Carolina. McGraw later said, "we might have to kill him" next time the protester shows up.

When asked about violence among his supporters, Trump insisted that anti-Trump demonstrators were instigating incidents at his campaign events.

“I certainly don’t incite violence," Trump said, echoing his words at Thursday night's GOP debate, when he said he hoped he wasn't encouraging violence at his rallies.

“If a protester is swinging a fist at a man or a group of men, and if they end up going back," he added, "I’m not looking to do him any favors."

Sen. Ted Cruz, who is Trump's closest rival in the race for the Republican nomination, took aim at Trump on Friday, and noted that "in any campaign responsibility starts at the top."

"When the candidate urges supporters to engage in physical violence, to punch people in the face, the predictable consequence of that is that it escalates," Cruz told reporters. "Today is unlikely to be the last such incidence."

Fellow GOP candidate John Kasich said Friday's events were the result of Trump sowing "seeds of division."

"Some let their opposition to his views slip beyond protest into violence, but we can never let that happen," the Ohio governor said in a statement.

Sen. Marco Rubio raised similar concerns about Trump's language at his rallies.

"There is only one presidential candidate who has violence at his events," Rubio told reporters. "I do think that Donald needs to realize and take responsibility for the fact that some of the rhetoric he has used could be contributing to this environment that is growing increasingly disturbing for a number of Americans."

Democratic front-runner Hillary Clinton said the "divisive rhetoric" of the Trump campaign should be of "grave concern."

"We all have our differences, and we know many people across the country feel angry," Clinton said in a statement. "We need to address that anger together."

Tensions flared in the days leading up to the rally, as students and faculty members signed a petition to stop the presidential hopeful's event. The petition garnered more than 50,000 signatures by Friday night.

Despite the mounting criticism, Chancellor Michael D. Amiridis said in a statement the university has no legal basis in barring any candidate from renting the event space.

UIC’s core values of freedom, equality and social justice for all, regardless of race, religion, national origin, disability status or sexual orientation, are deeply rooted in our diverse community and not endangered by the presence of any political candidate on campus. We encourage public and civic engagement by all members of our University and we endorse the idea that the answer to speech that one does not like or finds offensive is more speech and not censorship.

Attendees complained about the demonstrations that halted the event, suggesting they blocked Trump's right to free speech.

"This is ridiculous," Tom Keevers, a Trump supporter from the city's North Side, said after the cancellation was announced over the loudspeaker. "I'm a conservative. You wouldn't see conservatives shutting down a Hillary Clinton or Bernie Sanders rally!"

Trump officials announced on Friday that the campaign has scrapped plans, at least for now, for a rally in downtown Cincinnati on Sunday afternoon. He still has several rallies on his schedule for this weekend and into next week, including stops in Dayton, Cleveland, Bloomington, Ill., Kansas City, Mo., and Boca Raton, Fla.

The Secret Service security supporting the GOP presidential front runner's campaign could not complete its preparation work in time to hold the event at the Duke Energy Convention Center, said Eric Deters, a local spokesman for Trump's campaign.

"Trump wants to come here, and the campaign is still looking to find a location for either Sunday or Monday," Deters said.

Contributing: Jessica Estepa and Jason Williams

Follow USA TODAY Chicago correspondent Aamer Madhani on Twitter: @AamerISmad