Postponed green activity on course is discouraging (3-7)
I believe the answer is:
off-putting
'is discouraging' is the definition.
(I've seen this before)
'postponed green activity on course' is the wordplay.
'postponed' becomes 'off' (off can mean cancelled).
'green activity on course' becomes 'putting' (activity done on a green on a golf course).
'off'+'putting'='OFF-PUTTING'
(Other definitions for off-putting that I've seen before include "Discouraging" , "Disconcerting" .)