Many acts are beastly offensive (5)
I believe the answer is:
claws
'beastly offensive' is the definition.
(I've seen this before)
'many acts' is the wordplay.
'many' becomes 'c' (C is the Roman numeral for l00).
'acts' becomes 'laws' (law is a kind of act).
'c'+'laws'='CLAWS'
'are' acts as a link.
(Other definitions for claws that I've seen before include "beastly offensive" , "Grasping limbs, of a crustacean, say" , "Talons" .)