American Football Auckland (AFA) president Lani Ekepati said the supporter had reacted to a ruling by the official which he had taken offence to.
"A lot of these major sports games - it even comes down to the grass root games - it can always turn at the last second, you never say over until it's over," he said.
"It's really just came down to one person taking their actions without the support of others, that was separate entirely from the whole team, the whole club."
He said the injuries to the official's face had looked "pretty bad" and the man underwent an MRI scan while in hospital.
Mr Ekepati said clubs were responsible for controlling their own sideline support.
Following an emergency meeting last night, the organisation ruled the supporter would receive a lifetime ban - which could be appealed - from the sport.
"We take a big stance because it's a family sport, it's not just players involved, you've got families supporting, young kids.
"Controlled aggression is always in the game and sideline jurors, supporters, always have their own opinion, but at the end of the day it's up to the club to make sure they control their sideline."
Mr Ekepati said the incident was unfortunate, as it was not easy to find officials for the game. Compared to rugby, which has one referee, gridiron requires seven officials - and even with seven eyes on the field, rulings were still only around 87 to 89 per cent accurate, he said.
"Besides being the second most expensive sport in NZ, it's pretty hard to get people who want to officiate the games, let alone know how to officiate the games," he said.
It is understood police are investigating the incident.
