Parts loser messed up (5)
I believe the answer is:
roles
'parts' is the definition.
('role' can be a synonym of 'part')
'loser messed up' is the wordplay.
'messed up' indicates anagramming the letters.
'loser' anagrammed gives 'ROLES'.
(Other definitions for roles that I've seen before include "Parts in a play" , "Actors' parts" , "Theatrical parts" , "Dramatic parts" , "Parts in plays" .)