Our beast on the rampage, a wrecker (8)
I believe the answer is:
saboteur
'a wrecker' is the definition.
('saboteur' can be a synonym of 'wrecker')
'our beast on the rampage' is the wordplay.
'on the rampage' indicates anagramming the letters.
'our'+'beast'='ourbeast'
'ourbeast' with letters rearranged gives 'SABOTEUR'.
(Other definitions for saboteur that I've seen before include "Rebel" , "Vandal" , "Abort use (anag)" , "One causes damage to subvert" , "Oen who causes industrial damage for pay" .)