Punishes breaking into fields having much greenery (9)
I believe the answer is:
leafiness
'much greenery' is the definition.
(having a lot of leaves or greenery)
'punishes breaking into fields' is the wordplay.
'punishes' becomes 'fines' (punishes with a fine).
'breaking into' means one lot of letters goes inside another.
'fields' becomes 'leas' (lea can mean a field or meadow).
'fines' going inside 'leas' is 'LEAFINESS'.
'having' is the link.
(Other definitions for leafiness that I've seen before include "green growth" , "Forest will uphold such" .)