Jeanette described her reaction to hearing about the incident as "mother's fury" and said she had reported the incident to police.
"I wasn't actually at the game, so I didn't see what happened, McKenzie was knocked out cold so he doesn't remember anything ... he doesn't even remember the game.
"He just went straight down and was out for five minutes."
She said her son was now recovering at home.
"He's very sore, certainly not a happy chappy, we'll put it that way," she said.
"It was totally uncalled for, totally unprovoked, totally unnecessary.
"This kind of behaviour isn't in the nature of this sport at all and we would hate for it to happen to someone else and have suffered worse consequences and injuries than what Mac has got.
"Rugby is rugby and accidents happen and that's why the ref is there to control it but this just came out of the control of anyone."
A witness and spectator who wished to remain anonymous said Oliver had done nothing to provoke the attack.
"It was terrible. There was a scuffle going on in the game and there was only about five minutes to go, but Oliver was standing away from the incident and then this other chap who was the winger came from the other side of the field and from behind KO'd him in the side of the head.
"Oliver had nothing to do with the incident that was going on, which was under control pretty quickly. There just seemed to be complete astonishment from those watching."
The witness said the player was red carded, removed from the field and the game was stopped.
President of Napier Technical Rugby Jamie Bryant said they were "extremely embarrassed" by the player's behaviour.
"We'd like to offer the family our greatest apologies along with Central Rugby and Sports.
"This player has come from a 12-month suspension and as a club we've stood by him, got him along to anger management and now it's out of our hands for the way be behaved on Saturday," Bryant said.
"We can all do our best to stand by somebody and get them into the right frame of mind, but it clearly hasn't happened in this case.
"As far as I'm concerned and this club's concerned he's been kicked out of Napier Tech and I hope the actions of this player doesn't put a bad name on our club.
"We've had a fantastic relationship with Central Rugby and Sports and we'd like to continue that coming forward."