A schoolyard game involving flicking boys' testicles has elevated to a "full-fisted punch" to the groin and has landed at least two boys in Hawke's Bay Hospital this year.
The game, called "sac tap", which originally involved boys backhanding the testicles of others, had taken on a more disturbing and forceful development, according to a Taradale mother who believed her son's surgery was the result of a punch to his groin.
The mother, who did not want to be named, said she was worried the game was spreading through intermediate and high schools in Hawke's Bay.
"I'm not talking an open-handed hit but a full-fisted punch," the woman said.
"My son had it done to him a few times by a high school boy at a club he attends. He told him to stop it and the response was: 'You're too young for it to hurt.'
"My son says the game is dumb. The idea is that they walk up to someone and punch them in the groin by surprise."
The boy, who attends Tamatea Intermediate School, recently had surgery because of testicular torsion, a twisted testicle. He couldn't attend school for two weeks and missed out on playing sport as well.
His mother wasn't sure if the torsion was a result of being punched in the groin but a doctor she spoke to at the hospital told her he had seen about 10 similar cases in the past three weeks.
"I believe there must be a relationship there.
"I really want to get the message out to parents and caregivers to talk to their sons, schools and clubs to be aware and talk to the kids involved. Most importantly [talk to] the boys doing this, that it is not acceptable behaviour and could have a huge impact on someone."
Tamatea Intermediate School principal Roy Sye said the school had a crackdown on the game during term two but he was unaware the game now involved boys punching one another in the groin.
"This has come out of left field a bit for me and we have not come across any students punching each other. Last term, we called all of the boys together and male staff members, and made it clear that such behaviour is unacceptable in any shape or form."
Mr Sye said regardless of whether the game involved flicking or punching, it would not be tolerated.
"We take any form of assault seriously. It is a stupid game and I've got no idea where it came from. My door is open to parents who have concerns, to come in and talk to me."
Hawke's Bay Hospital's urology consultant David Mason said he was aware of the practice which had been "unfortunately" occurring in high schools for several years.
Mr Mason said he had treated two students this year for pain as a result of the game but said it was unlikely it would cause a twist, or torsion, of the testicle.
"More commonly it would cause pain, swelling and if the hit was hard enough, could cause the testicle to rupture."