After the final whistle, a spectator - who appeared to be related to the player - approached the referee to speak with him.
Following their discussion "the young ref went to walk away and was blindsided by a hit to his chin that landed him on the ground", the witness said.
The spectator "then tried strangling him - picking the ref up by the throat".
Other parents quickly ran on to the field to intervene.
It was the second such incident last Saturday - an Otago club player punched a young referee who had handed him a red card. Police yesterday charged a 27-year-old man with assault over the incident.
Police are investigating the incident.
An independent judicial hearing would be held in parallel with that criminal investigation.
Counties Manukau Rugby Football Union chief executive Barton Hoggard told the Weekend Herald that the young referee was recovering from the "horrible" incident.
"(he) is well, all things considered, and he is being fully supported by employees of our union as well as the Steelers which is our Mitre 10 Cup team," he said.
"This was a horrible incident and one that we obviously do not condone.
"We are fully supporting the referee and we are currently conducting our own investigation.
"We take the safety of our referees, players and supporters very seriously which is why we are so appalled by this incident."
Hoggard said alongside the investigation, a full review of union policies was under way.
"We are in the process of reviewing what other policies and practices can be put in place to ensure that referees, players and supporters are in a safe environment," he explained.
"In practice, it is the clubs and the event managers that are on the frontline ensuring that the people on their grounds are behaving in accordance with the relevant club's rules as well as the rules prescribed by New Zealand Rugby and Counties Manukau Rugby Football Union."
He has sent a strong message to CMRFU club network ahead of this weekend's matches, reiterating the "appalling" behaviour last week.
"All of us need to be proactive in ensuring that this does not occur again at any of our clubs," he said.
"The clubs need to ensure that all of their teams have event managers at each of their games and that these event managers take their roles seriously and ensure that their team's parents and supporters behave in an appropriate and respectful manner at all times.
"Event managers are not a new initiative – we just need all of our event managers to carry out their role in a vigilant manner to ensure that we avoid a repeat of what happened."
He said everyone had a part to play in improving culture and preventing future incidents.
"The behaviour that you turn a blind eye to, is the standard that you accept - and this then becomes the cultural norm," he told the clubs.
"So please do not turn a blind eye to any disrespectful behaviour towards our referees.
"This incident has to be a trigger for positive behavioural change."
Earlier this week Ardmore Marist club president Glenn Flavell said the spectator involved was not a club member.
He declined to comment further, saying he was mindful of the "human impact" of the incident and wanted to ensure everyone respected the investigation.
