Loser exchanged parts (5)
I believe the answer is:
roles
'parts' is the definition.
('role' can be a synonym of 'part')
'loser exchanged' is the wordplay.
'exchanged' is an anagram indicator.
'loser' is an anagram of 'ROLES'.
(Other definitions for roles that I've seen before include "Theatrical parts" , "Dramatic parts" , "Parts in plays" , "Parts in a play" , "Actors' parts" .)