"Violence in any form is unacceptable, particularly when witnessed by children, and police will investigate."
The Otago Daily Times understands the coach of one of the teams at Bathgate Park had just finished refereeing the game when he was allegedly assaulted.
A member of the Kaikorai junior club detailed the incident and the aftermath in a Facebook post.
"Pretty hard to write this report as our young kids were left in tears after being exposed to some of the most disgusting behaviour from the sidelines that I have ever witnessed.
"Swearing, threats, and my co-coach/ref taking a punch to the face."
Southern club chairman Blair Crawford said yesterday he had been made aware of the incident.
"Naturally, any allegation of assault we take very seriously," Crawford said.
"We are gathering as much information as we can from those involved in this junior game and will be working alongside our junior club to make sure this is dealt with appropriately.
"Due process has to take place first, but there is no tolerance for any type of assault that has been alleged."
Otago Rugby Football Union chief executive Richard Kinley said he was aware of the Bathgate Park incident.
However, it was "inappropriate to comment" until he had more information, he said.
He was also aware of the incident involving the secondary schoolboys' manager but understood the matter had been dealt with by the respective schools.
Kinley said the union took every incident seriously.
"Any incident is one incident too many," Kinley said.
There appeared to be a national rise in incidents of bad behaviour on sporting sidelines but Otago supporters were generally well behaved, he said.
"Throughout the country, through all sports, there seem to be more incidents occurring, and I don't know what the reason for that is," Kinley said.
"Otago sport, in general, has been pretty good.
"If you look at Saturday sport across the province, hundreds and hundreds of games of various sports are going ahead in good spirits, with everyone having a good time.
"Unfortunately, you get these things — I hope they are one-offs — that affect everybody."