Fall, getting nothing to sag (5)
I believe the answer is:
droop
'to sag' is the definition.
(synonyms)
'fall getting nothing' is the wordplay.
'fall' becomes 'drop' (synonyms).
'getting' is an insertion indicator.
'nothing' becomes 'O' (O resembles 0).
'drop' placed around 'o' is 'DROOP'.
(Other definitions for droop that I've seen before include "Decline" , "sink" , "Dangle" , "Sag downwards" , "male problem?" .)