Playing roles one hasn't won (5)
I believe the answer is:
loser
'one hasn't won' is the definition.
Although both the answer and definition are singular nouns, I can't understand how they can define each other.
'playing roles' is the wordplay.
'playing' is an anagram indicator.
'roles' is an anagram of 'LOSER'.
Can you help me to learn more?
(Other definitions for loser that I've seen before include "lemon" , "A failure, also-ran" , "Failed competitor" , "Unsuccessful competitor" , "One who regularly fails" .)