Top playing field that's long (4)
I believe the answer is:
itch
'that's long' is the definition.
(to long or itch for something is to desire it)
'top playing field' is the wordplay.
'top' means to remove the first letter.
'playing field' becomes 'pitch' (I've seen this before).
'pitch' with its first letter taken away is 'ITCH'.
(Other definitions for itch that I've seen before include "Feel tingling sensation in skin" , "It needs to be scratched" , "Constant desire" , "Longing; anag. of 19" , "Contagious skin infection" .)