Singer, a large guy, tucking into booze (9)
I believe the answer is:
balladeer
'singer' is the definition.
(someone singing ballads)
'a large guy tucking into booze' is the wordplay.
'large' becomes 'L' (eg in clothes sizes).
'guy' becomes 'lad' (both can mean a man or boy).
'tucking into' is an insertion indicator.
'booze' becomes 'beer'.
'a'+'l'+'lad'='allad'
'allad' inserted inside 'beer' is 'BALLADEER'.
(Other definitions for balladeer that I've seen before include "Minstrel" , "One sings" , "pop singer" , "One making a song" .)