Parents at a Minnesota elementary school were alarmed to learn about a disturbing new playground game that was apparently all the rage at recess: Rape tag.

Principal Bill Sprung of Washington Elementary School in New Ulm, Minn. sent a letter home to parents Monday alerting them to the game, described as “similar to freeze tag except that a person had to be humped to be unfrozen.”

According to the letter, the game was played mainly by fifth grade students in two specific classrooms. Teachers were instructed to speak to their classes about not playing the game, and recess supervisors were told to watch for any incidents of it.

A parent first alerted Sprung to the game on Jan. 10, but he only decided to send the letters home after rumors about how it was played began swirling on Facebook. In one variation, Minnesota CBS affiliate WCCO-TV reported children were encouraged to tag each other “by pulling the other child’s private parts.” A separate WDAY-TV report stated the player who was “it” was “the rapist” and instead of saying “you’re it” would say “rape,” and get points for touching people on certain body parts.

According to Minnesota Fox affiliate KMSP-TV, Sprung said the school had already put a stop to the game but decided to send the letter to tamp down on the “distorted” versions.

“There was so much misinformation that was going on, parents started publishing lists of kids who might have been playing…the embellishment about the game really became extreme,” he said.

Still, Sprung praised school employees for taking swift action to put an end to the game on the playground.

“I think in terms of extinguishing the game, the school and the staff did an excellent job,” Sprung told MSNBC.