Loser's replacement parts (5)
I believe the answer is:
roles
'parts' is the definition.
(parts in a play)
'loser's replacement' is the wordplay.
'replacement' indicates anagramming the letters.
'loser' with letters rearranged gives 'ROLES'.
(Other definitions for roles that I've seen before include "Theatrical parts" , "Dramatic parts" , "Actors' parts" , "Parts in a play" , "Parts in plays" .)