"Look, injuries happen with sport. We have about a dozen breaks a year and that's playing sport, playing at lunchtime, PE lessons. I don't want to get into 'Is it a good thing, banning bullrush' or anything like that. That's just what kids do.
"Everyone was willing participants, but sadly, some boys got hurt. It's a real pain for those boys, going into summer with an injury."
Mr Hill said he was standing alongside teachers watching the games on the field this week when the injuries occurred.
The broken bones were discovered after school hours and no ambulances attended the school grounds, he said.
"I was out there, I was really enjoying the way the kids were interacting, actually. Obviously, I didn't enjoy anyone getting hurt.
"There were lots of different games going on on the front field. It wasn't one bullrush game of 1300 boys. That happens here every day, there are lots of games of touch or scrag or league or bullrush. It's a great time of the year when kids are out on the fields."
A mother at the school told Fairfax she heard there was a "charge attack" on juniors organised by seniors at the school during the bullrush game on Tuesday. She had also heard laptops were broken in the game.
"If one of those was my son I certainly wouldn't be thinking it was good natured. As a mother at a boy at the school I am horrified at this. How could the school condone that," she said.
But Mr Hill said that was not the case.
"It might have been kids chasing other kids and tackling them, but everyone was a willing participant," he said.
An assembly had been held to remind senior students to be careful when playing with juniors, he said.
Bullrush has been dubbed "rugby without a ball" and involves students running and attempting to tag or tackle each other.
The pastime was banned from most schools in the 1990s after safety concerns arose, but a push-back against wrapping kids in cotton wool saw principals slowly reintroduce the game.
Principal Scott Thelning brought back the banned game back to two Christchurch primary schools in 2013.
"One of the lasting memories of primary school I have is the day I tackled the biggest kid and just dived at his legs and hoped for the best," Mr Thelning told the Herald at the time.
"We are always talking about encouraging our students to be risk-takers ... and then we ban and limit things and mollycoddle them ... How do they assess risk if we don't let them?"