Fine stag possibly eating well (8)
I believe the answer is:
feasting
'eating well' is the definition.
(I've seen this before)
'fine stag possibly' is the wordplay.
'possibly' indicates anagramming the letters.
'fine'+'stag'='finestag'
'finestag' is an anagram of 'FEASTING'.
(Other definitions for feasting that I've seen before include "Eating well" , "Eating a large meal" , "Eating and drinking lavishly" .)