CHICAGO (AP) — Republican presidential candidate Donald Trump canceled one of his signature rallies on Friday, calling off the event in Chicago out of safety concerns after protesters packed into the arena where it was to take place.

The announcement that the billionaire businessman would postpone the rally until another day led a large portion of the crowd inside the University of Illinois at Chicago Pavilion to break out into raucous cheers. Meanwhile, supporters of the candidate started chanting “We want Trump! We want Trump!”

There were isolated physical confrontations between some members of the crowd after the event was canceled.

There was no sign of Trump inside the arena on the college campus, where dozens of UIC faculty and staff had petitioned university administrators to cancel the rally. They cited concerns it would create a “hostile and physically dangerous environment” for students.

Before the announcement the event wouldn”t take place, a handful of intense verbal clashes took place between Trump supporters and protesters as the crowd waited for his arrival.

For the first time during his White House bid, the crowd appeared to be an equal mix of those eager to cheer on the real estate mogul and those overtly opposed to his candidacy.

When one African-American protester was escorted out before the event started, the crowd erupted into chants of “Let them stay!”

Veronica Kowalkowsky, an 18-year-old Trump supporter, said before the event started that she had no ill will toward the protesters — but didn”t think they felt the same way.

“I feel a lot of hate,” she said. “I haven”t said anything bad to anyone.”

Hours before the event was scheduled to start, hundreds of people lined up outside the arena at the University of Illinois at Chicago — a civil and immigrant rights organizing hub with large minority student populations. Trump backers were separated from an equally large crowd of anti-Trump protesters by a heavy police presence and barricades.

Some Trump supporters walking into the area chanted, “USA! USA!” and “Illegal is illegal.” One demonstrator shouted back, “Racist!”

One protester, 64-year-old Dede Rottman of Chicago carried a placard that read: “Build a Wall Around Trump. I”ll Pay for it.”

However, 19-year-old Rusty Shackleford of Lombard, in line to attend the Trump rally, said he was there to “support the man who wants to make America great again.”

Chicago community activist Quo Vadis said hundreds of protesters had positioned themselves in groups around the arena, and that they intended to demonstrate right after Trump took the stage. Their goal, he said, is “for Donald to take the stage and to completely interrupt him. The plan is to shut Donald Trump all the way down.”

Earlier in the day, Trump taunted the protesters in St. Louis from the stage at the city”s Peabody Opera House, even as he promised that police and security would be “gentle” as they removed them.

“They”re allowed to get up and interrupt us horribly and we have to be very, very gentle,” Trump said in response to one of the interruptions. “They can swing and hit people, but if we hit them back, it”s a terrible, terrible thing, right?”

He panned the protesters as weak “troublemakers,” ordered them to “go home to mommy” or “go home and get a job” because “they contribute nothing.”

“These are not good people, just so you understand,” Trump said. “These are not the people who made our country great. These are the people that are destroying our country.”

As Trump attempts to unify a fractured Republican Party, racially charged images of his supporters attacking protesters and allegations that he”s inciting violence have cast new attention on the divisive nature of his candidacy.

It intensified this week, when a North Carolina man was arrested after video footage showed him punching an African-American protester being led out of a rally in that state on Wednesday. At the event, the billionaire real estate mogul recalled a past protester as “a real bad dude.”

“He was a rough guy, and he was punching. And we had some people — some rough guys like we have right in here — and they started punching back,” Trump said. “It was a beautiful thing.”

Friday”s gathering in St. Louis was his first public campaign event since, and Trump defended his conduct and lashed out at the press for making too much of the clashes.

“You know, they talk about a protest or something. They don”t talk about what”s really happing in these forums and these rooms and these stadiums,” Trump said. “They don”t talk about the love.”

He added that he and his supporters aren”t angry people, but they “do get angry when we see the stupidity with which our country is run and how it”s being destroyed.”

“I”d rather be too strong than too weak, by a long shot,” he said.