DENVER – Nearly 30 Air Force Academy cadets required medical care, with six of them hospitalized, after an annual tradition to mark the first snowfall of the season turned into an out-of-control melee, school officials said on Wednesday.

An unauthorized ritual last week called “First Shirt/First Snow,” in which freshman cadets try to throw their cadet sergeant into a snowbank, grew violent and resulted in injuries, the academy said in a statement.

“A relatively small number of cadets chose to take part in this unsafe activity,” Brigadier General Gregory Lengyel said. “This incident was unacceptable.”

The six cadets who required hospitalization after last Thursday’s incident have all been released, and the 21 others were treated for “bruises and/or lacerations” at the academy’s cadet clinic, the school said.

Lengyel, who serves as the commandant of cadets, said school officials are investigating the incident. “Our Air Force expects better. I expect better, and I’m confident the cadets will learn and grow from this.”

An internal email about the incident obtained by the Air Force Times newspaper, reportedly written by Brigadier General Dana Born to school administrators, said the annual ritual “has turned into a brawl” between freshmen and upperclassmen.

“This ritual has devolved to become increasingly violent, with significant numbers of cadets requiring medical care over the past two years,” The Times cited the email as saying, adding that the latest injuries included concussions, an arm bite and cuts that required stitches.

The Times said the internal memo indicated Lengyel might allow the tradition to continue if cadets can show it can be conducted with “good order and discipline and proper risk management.”

Located in Colorado Springs, 60 miles south of Denver, the academy has an enrollment of about 4,100 cadets, and graduates are commissioned second lieutenants in the U.S. Air Force.

(This story is corrected with rank of graduates in final paragraph)

(Editing by Steve Gorman and Todd Eastham)