Injure badly by beating (4)
I believe the answer is:
maul
'injure badly by beating' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for maul that I've seen before include "Wound by scratching and tearing - rugby move" , "Treat roughly; heavy hammer" , "Handle roughly, batter" , "Pummel" , "Loose 10 (in rugby)" .)