Drinker wanting best beer, just half (5)
I believe the answer is:
toper
'drinker' is the definition.
(I know that drinker can be written as toper)
'wanting best beer just half' is the wordplay.
'wanting' means one lot of letters go next to another.
'best' becomes 'top' (top can mean the very best).
'just half' indicates taking half.
'beer' halved is 'er'.
'top' next to 'er' is 'TOPER'.
(Other definitions for toper that I've seen before include "Drunkard" , "Someone with a drink problem" , "Serious drinker" , "Soak" , "Drinker, imbiber" .)