Lap up wallop (4)
I believe the answer is:
lick
I believe this clue is a double definition.
'lap up' is the first definition.
(thesaurus)
'wallop' is the second definition.
(I've seen this in another clue)
(Other definitions for lick that I've seen before include "Lap; beat soundly" , "Taste" , "A - - and a promise" , "little paint" , "Flog" .)