Composer's drunk lager (5)
I believe the answer is:
elgar
'composer's' is the definition.
(Edward Elgar)
'drunk lager' is the wordplay.
'drunk' is an anagram indicator.
'lager' anagrammed gives 'ELGAR'.
(Other definitions for elgar that I've seen before include "British composer, d. 1934" , "Glare at composer of 'The Dream of Gerontius'" , "Land of Hope and Glory composer" , "[NIMROD] 's creator" , "He scored" .)