Hi John.
'Rub of the green' means the 'grain' or direction that cloth/grass etc are lying in (e.g. snooker or golf) and has some effect on how the balls run across the surface.
Only really good players even worry about it in any rational way, but amateurs may, if they have some good luck, possibly say that they have the 'rub of the green'?
Personally, I just hit & hope.
JimC