Failure more relaxed missing an Oscar (5)
I believe the answer is:
loser
'failure' is the definition.
(someone who has failed)
'more relaxed missing an oscar' is the wordplay.
'more relaxed' becomes 'looser' (loose can mean relaxed or casual).
'missing' is a deletion indicator.
'an oscar' becomes 'O' (phonetic alphabet: alpha, bravo, charlie etc.).
'looser' with 'o' removed is 'LOSER'.
(Other definitions for loser that I've seen before include "one plays without success" , "One who is always a failure" , "One failing regularly" , "Unsuccessful person" , "One who is (always) unsuccessful" .)