In the auditorium, spoils string instrument (4)
I believe the answer is:
'string instrument' is the definition.
(type of stringed instrument)
'in the auditorium spoils' is the wordplay.
'in the auditorium' shows a homophone (sound like) (ie as heard on a stage).
'spoils' becomes 'loot' (both can mean a reward or proceeds).
'loot' is a homophone of 'LUTE'.
(Other definitions for lute that I've seen before include "Old stringed instrument with a pear-shaped body" , "Protective packing" , "Plucked, pear-shaped instrument" , "Play instrument" , "Old musical instrument" .)