The incident was part of a long-running rivalry between two Oamaru boys' schools, and left one of the intruders with a broken collarbone.
The tribunal said a "red mist" descended on Justin Fowler, the then-assistant principal and director of boarding at St Kevin's College in Oamaru, when he saw people throwing eggs at vehicles and buildings at the school in June 2020.
In the resulting pursuit one of his pupils tackled an 18-year-old, breaking the young man's collarbone.
Police referred the pupil to its youth aid section for assault, along with the intruder.
The tribunal said Fowler accepted wrongdoing but did not accept that his actions were serious misconduct.
But the tribunal's complaints assessment committee, which brought the case to the tribunal, described his actions as "an extreme overreaction to young people coming on to the college grounds to play pranks".
It also alleged Fowler put his pupils in a dangerous situation because he did not know who the intruders were.
The tribunal rejected Fowler's defence that he was protecting his school and family, and said he was acting out of anger and a desire for retribution.
It said Fowler put his pupils in a difficult situation and they assaulted a person at his direction.
"What cannot be overlooked is that the respondent persuaded impressionable students to use physical force against others. One man was injured. The respondent could have and should have shown better judgement and tried to deescalate the situation," it said.
It said his actions potentially put his pupils in harm's way.
The tribunal censured Fowler, ordered him to complete behaviour or anger management courses, and banned him from any management or leadership positions for 12 months.
It said the incident happened around the time of an annual rugby match with Waitaki Boys' High School. It said there was a history of violence and disorder around the match, though the two schools had worked hard to address it.
St Kevin's College said in a statement that as per the ruling, Fowler was no longer the school's assistant principal.
"The health and wellbeing of our students is always at the forefront of our thinking," it said.
"We have assured the community that we have made a detailed investigation into the event and have taken measures, along with other local schools, to minimise future harm. For example we have hired extra security around the school during the week leading up to the match to prevent a repeat of the incident."