Trophy holds nothing but success (4)
I believe the answer is:
coup
'success' is the definition.
(coup can mean a success or triumph)
'trophy holds nothing' is the wordplay.
'trophy' becomes 'cup' (cup is a kind of trophy).
'holds' means one lot of letters goes inside another.
'nothing' becomes 'O' (looks like zero - 0).
'cup' enclosing 'o' is 'COUP'.
'but' is the link.
(Other definitions for coup that I've seen before include "Accomplishment, exploit" , "Masterstroke" , "Successful stroke or action - could be d'etat" , "Sudden change, illegally or by force" , "Hostile takeover" .)