Group deny act is revolting (9)
I believe the answer is:
syndicate
'group' is the definition.
(syndicate is a kind of group)
'deny act is revolting' is the wordplay.
'revolting' indicates anagramming the letters.
'deny'+'act'+'is'='denyactis'
'denyactis' anagrammed gives 'SYNDICATE'.
(Other definitions for syndicate that I've seen before include "Team" , "Business group supplied by CIE dynast" , "Affiliated group" , "Group of promoters with a common interest" , "Organised group of individuals" .)