"I can't see any particular reason why they would be up at this time of year," he said.
"A couple of weeks ago there was quite a burst of them that had us wondering what was going on.
"I was at a referees' meeting last night and there was no specific aspect apart from repeated infringements - and that's just playing and coaching attitude - or trying to prove a point as individuals and as a team in the first months of the competition."
Greenstreet said there had been no directive issued to referees at the beginning of the competition relating to placing greater emphasis on any area of foul play, but noted that infringements at the breakdown and illegal tackles constitute the majority of offences that see players sidelined.
As of Saturday, Opotiki had received the most yellow cards with eight, with Mount Maunganui and Rangiuru in second place with seven apiece.
Tauranga Sports were the next on the list with six, while Judea had been shown five.
Community rugby administrator Yvonne Jarvis said each registered player has a record showing past indiscretions that is referenced whenever they appear in front of the judicial panel.
A second yellow card in the same season is followed by a letter from the rugby union.
"If they get two yellow cards I write to them to tell them they are on a warning. If they get another one it's an automatic one week stand down."
The guidelines for disciplinary matters - which share many similarities to the grading system used in both professional rugby union and rugby league - have been passed down by the New Zealand Rugby Union in a 56-page booklet including everything from rules and regulations to forms for referees to fill out in the event of an abandoned match.
It lists the entry point and maximum penalties for almost every indiscretion, from verbal abuse and spitting to striking with the head and physically assaulting match officials.
Provisions have been made for life bans for players who assault referees or touch judges, with the maximum penalty for threatening officials standing at 260 weeks.
A player can receive a maximum of 208 weeks on the sideline for "testicle grabbing or twisting or squeezing", biting and contact with the eyes or eye area, and a maximum of 104 weeks for striking with the head or providing false or misleading information to officials.
Maximum 52-week penalties are in place for a number of offences ranging from hair pulling and spitting to verbally assaulting players based on "religion, race, colour, national or ethnic origin, sexual orientation or otherwise".