A variation of the game of freeze tag ominously named “rape tag” has alarmed administrators and parents at an elementary school in Minnesota, after the principal was notified by a concerned parent earlier in the month.

Principal Bill Sprung of Washington Elementary School in New Ulm sent a letter home this week to parents to inform them of the disturbing game, which was described as similar to freeze tag, “except that a person had to be humped to be unfrozen,” the letter states.

After being notified about the incident, which involved students in two classrooms, Sprung immediately informed teachers and recess supervisors to talk to students about the matter and put an end to the game, writes Sylvia Wood at MSNBC.

“We addressed it as an inappropriate game,” he said.

While officials say that there has been no recurrence of the game since they were notified, rumors and speculation apparently fueled by Facebook postings caused Sprung to choose to send letters home.

Sprung has defended the way that the school has handled the matter:

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

“Since the surge in facebook discussions, all staff at Washington has been notified of the game and will be watching for any incidents of the game.”

Around 20 parents got back in touch with Sprung after they had received the letter, saying that they were upset about having to discuss the sensitive topic with their children, reports Wood.

The incident may have shocked parents and officials alike, but Sprung has chosen not to increase the amount of playground supervision.

“We have not needed to increase the monitors,” he said.