"He loved his rugby.''
Mr Mills had been a premier grade referee for Marlborough some years ago, but was now refereeing games when needed.
"He's filled in over recent years when someone can't make it or there's a gap,'' Mr Bancroft said.
Mr Mills had been a dairy farmer on a farm in Koromiko, between Blenheim and Picton until he retired about a year ago.
He had since been working on vineyards in the region, Mr Bancroft said.
Referee Education Officer for the Tasman Rugby Union Nigel Jones said Mr Mills had for a long time been an important part of the sport in the region.
"Peter had been a valued member of the referee association."
Sergeant Jason Munro of Blenheim Police said bystanders and parame``ics performed CPR for around 50 minutes to no avail.
"He was well-known and well-respected and it was obviously distressing for everybody,'' Mr Munro said.
The young players were moved from the field when he collapsed, Mr Munro said.