Hat quietly grabbed by heavy drinker (6)
I believe the answer is:
topper
'hat' is the definition.
(topper is a kind of hat)
'quietly grabbed by heavy drinker' is the wordplay.
'quietly' becomes 'p' (p for piano and quiet).
'grabbed by' indicates putting letters inside.
'heavy drinker' becomes 'toper' (I've seen this before).
'p' placed within 'toper' is 'TOPPER'.
(Other definitions for topper that I've seen before include "expensive hat" , "Informally a tall hat - the best" , "Top hat (colloq.)" , "Man's hat with a tall crown" , "good sort" .)