Upstart coming in drove bad wolf down (6)
I believe the answer is:
devour
'wolf down' is the definition.
(I know that devour is a more specific form of the action the wolf down)
'upstart coming in drove bad' is the wordplay.
'upstart' becomes 'u' (start of the word 'up').
'coming in' means one lot of letters goes inside another.
'bad' indicates anagramming the letters.
'drove' anagrammed gives 'devor'.
'u' placed inside 'devor' is 'DEVOUR'.
(Other definitions for devour that I've seen before include "Eat hungrily and quickly" , "Gobble up greedily" , "Eat greedily" , "Guzzle" , "Read avidly" .)