Sulky look when nothing is in place (4)
I believe the answer is:
pout
'sulky look' is the definition.
(I've seen this in another clue)
'nothing is in place' is the wordplay.
'nothing' becomes 'O' (O resembles 0).
'is in' is an insertion indicator.
'place' becomes 'put' (synonyms).
'o' going within 'put' is 'POUT'.
'when' is the link.
(Other definitions for pout that I've seen before include "Purse lips sulkily" , "Look miffed" , "Push out one's lips" , "Push lips out in petulance" , "shows disappointed face" .)