Prevent trophies being sent back (4)
I believe the answer is:
stop
'prevent' is the definition.
(stopping is a kind of preventing)
'trophies being sent back' is the wordplay.
'trophies' becomes 'pots'.
'being sent back' is a reversal indicator.
'pots' back-to-front is 'STOP'.
(Other definitions for stop that I've seen before include "Close < finish" , "It could be the organist's principal" , "Check" , "Pack it in - bar" , "Cease; organ voice" .)