Belt required when stout, with nothing left to tuck in (9)
I believe the answer is:
bandoleer
'belt' is the definition.
(bandoleer is a kind of belt)
'stout with nothing left to tuck in' is the wordplay.
'stout' becomes 'beer'.
'with' becomes 'and'.
'nothing' becomes 'O' (looks like zero - 0).
'left' becomes 'l' (common abbreviation).
'to tuck in' is an insertion indicator.
'and'+'o'+'l'='andol'
'beer' placed around 'andol' is 'BANDOLEER'.
'required when' acts as a link.
(Other definitions for bandoleer that I've seen before include "Shoulder belt" , "Ammunition holder" .)