Police were called to Napier Boys High' School this afternoon after an apparent assault on a student by one of up to three young males who came on to the school grounds.
School principal Matthew Bertram said a student was punched before the offender was "locked-down" by another student.
Police confirmed they were called about 2.30pm, and while investigations were continuing no one had been arrested by late afternoon.
Bertram said the incident appeared to be "over a girl".
The student was being supported at the school awaiting the arrival of a parent, while extra staff were present on the Chambers St frontage of the school to monitor after-school activity outside Hawke's Bay's biggest school, which has a roll of about 1200.
Numbers on the school grounds more than doubled during the day for the first rounds of the national secondary schools' Under-15 rugby championship, with teams from 16 schools from as far afield as Auckland and Dunedin.
While the altercation is thought to have been seen by some of the visitors, police and the school believe it was not linked to the event.