The boy, who attends Tamatea Intermediate School, recently had surgery because of testicular torsion, a twisted testicle.
His mother wasn't sure if the torsion was a result of being punched in the groin but a doctor at the hospital told her he had seen about 10 similar cases in the past three weeks.
"I really want to get the message out that it is not acceptable behaviour and could have a huge impact on someone," she said.
Tamatea Intermediate principal Roy Sye said it had a crackdown on the game but was unaware it now involved boys punching one another in the groin.
Hawke's Bay Hospital urology consultant David 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.