Police Chief Calvin Williams was among a dozen officers trying to restore order by pushing people back.
Earlier in the day, blocks away from the arena, a right-wing religious group lifted a banner reading “Jesus is angry with you sinners,” while kissing lesbians mocked their message, helping turn Cleveland’s Public Square into part-carnival, part-debate floor.
The expansive square was a free-flowing mix of ideas and beliefs along with colorful characters pounding on bongos and wailing on a sousaphone.
The day’s demonstrations started with a few dozen people holding banners printed with a red-brick design and forming a human wall to mock Donald Trump’s plan to seal off the Mexican border.
“We want to wall off the hate of Trump,” said Tim Chavez, of Columbus.
A half-dozen Trump supporters defended the GOP nominee from attacks by immigration activists.
Police officers used bicycles and their bodies to separate those with opposing views.
Jesse Gonzalez, of Lakewood, a Cleveland suburb, carried a rifle on Public Square while wearing a camouflage-style “Make America Great Again” hat. Ohio law allows gun owners to carry their weapons openly.
“I’m out here to illustrate that not all gun owners, if any or very few, are irresponsible or uneducated,” he said.
Before the flag-burning protest turned violent, police said five people had been arrested since the start of the convention.
That includes one person accused of trying to steal a state trooper’s gas mask and three people charged with climbing flagpoles at the Rock and Roll Hall of Fame and hanging an anti-Trump banner.
Associated Press writer Mark Gillispie contributed to this report.