Two teenage girls apparently started hitting each other at Michael R. White Elementary School, and their families joined in, Cleveland police Cmdr. Wayne Drummond said. The fight involved adults and minors, he said.
"You had adults fighting adults, juvies fighting juvies, and so forth," he said as parents streamed into the building to pick up their children. "You just had a melee here."
No one was hurt, Drummond said.
No charges were immediately filed, but those arrested were being booked for aggravated rioting, Drummond said. By city practice, charges are filed after prosecutors review a case.
A parent of students at the school, Brianna Smith, went was alerted by a neighbour about the fight and went to the school to get her 7- and 12-year-old sons. "It makes me not want to send them for the rest of the school year," she told The (Cleveland) Plain Dealer.
City Councilman Jeff Johnson lives across the street from the school, which is in a blue-collar neighbourhood overlooking the leafy University Circle arts and museum district. He said the spilled punch set off the fight, with one person pulling out a pipe and another a hammer, leading school security officers to call police.
"Mouthing off, one thing leads to another and it spills out here," Johnson said.
At least 10 patrols cars went to the scene.
"It was a very chaotic scene," according to Drummond, who said the fight erupted as the ceremony was ending about 11 a.m. and then moved outside.
Officers quickly restored order, Drummond said. More than the eight arrested were involved in the fight, and the initial heavy police response came amid a call, which turned out to be false, about shots fired, he said.
No students enrolled at the school were involved, school district communications officer Roseann Canfora said in an email.
The school was put on lockdown and parents began arriving to take their children home.
Johnson said the quick police response was important amid heightened concerns about school security.
"It is embarrassing that parents during a kindergarten promotion cannot control themselves, and what we tried to do was respond significantly," he said.
Any parent involved in the fight should be banned from the building, Johnson said. "We're not going to have people coming into our schools, being disrespectful, fighting. So I support them being hauled off," he said.