Beat fellow with lump of wood (4)
I believe the answer is:
flog
'beat' is the definition.
(flogging is a kind of beating)
'fellow with lump of wood' is the wordplay.
'fellow with' becomes 'f' (I've seen this in other clues).
'lump of wood' becomes 'log' ().
'f'+'log'='FLOG'
(Other definitions for flog that I've seen before include "- - a dead horse" , "Beat with whip or slangily sell" , "Exchange for money" , "Scourge, whip" , "Whip severely" .)