Splendid drink knocked over (5)
I believe the answer is:
regal
'splendid' is the definition.
(I've seen this in another clue)
'drink knocked over' is the wordplay.
'drink' becomes 'lager' (lager is a kind of drink).
'knocked over' is a reversal indicator.
'lager' written backwards gives 'REGAL'.
(Other definitions for regal that I've seen before include "Kingly or queenly" , "Imperial, majestic" , "Kingly glare?" , "King-like" , "King's" .)