The incident occurred just before lunchtime during Norway Cup – one of the world's largest youth tournaments in football with 30,000 participants from 35 countries.
The referee, a man in his 50s, is said to have been hit in the head by a spectator during a match and was taken to hospital with serious injuries.
It becomes a form of brawl and in the incident, the referee is exposed to violence, says the police's operational leader Mikael Dellemyr to journalists on site at the football cup.
According to the match's main referee, it was after the assistant referee tried to remove a spectator that the situation escalated. The referee then received a blow to the face and fell to the ground, he says to VG.
He lay there for five minutes.
The perpetrator, a Spanish citizen in his 20s, is not believed to have any connection to either of the teams that played the match in question.
"We are currently working to get an overview and the case is being handled by the police," says Hanne McBride, communications manager at Norway Cup, in a statement to several media outlets.
The perpetrator fled the scene on foot but was arrested by the police at 11:50.
The man will spend the next period of time in police custody.
We do not want to hold him longer than necessary, but we must also be able to investigate the case without him leaving the country, says Mikael Dellemyr.
