Common sense to be honest. Although not everything Miramar did was above board - Wairarapa's Sam Mason-Smith turned out for Miramar in Cap 9 so remains to be seen if this stops them.
Edit: or was he a Wairarapa player at that time?
This will get all clubs -
Any player who reaches 66% of league matches for any one team cannot re-grade down again to a team in a lower division for the remainder of that season. This includes players who have played 66% of Central League matches entering into a tier 1 team.