Sinking Smith's top bitter, litre drunk (9)
I believe the answer is:
scuttling
'sinking' is the definition.
(scuttle can mean to sink or scurry away)
'smith's top bitter litre drunk' is the wordplay.
'top' says to take the initial letters.
'bitter' becomes 'cutting' (both can mean acerbic).
'litre' becomes 'L' (abbreviation).
'drunk' means one lot of letters goes inside another (inserted letters are drunk in).
The initial letter of 'smiths' is 's'.
'cutting' enclosing 'l' is 'cuttling'.
's'+'cuttling'='SCUTTLING'
(Other definitions for scuttling that I've seen before include "Dashing about and sinking the ship" , "Destroying" .)