Aggressor's press release to editor returning duty list (8)
I believe the answer is:
predator
'aggressor's' is the definition.
(predator is a kind of aggressor)
'press release to editor returning duty list' is the wordplay.
'press release' becomes 'pr' (public relations).
'to editor' becomes 'ed'.
'returning' is a reversal indicator.
'duty list' becomes 'rota' (I've seen this before).
'rota' backwards is 'ator'.
'pr'+'ed'+'ator'='PREDATOR'
(Other definitions for predator that I've seen before include "eagle, say" , "Exploitative person" , "Hunting animal" , "Hunter" , "eg 19" .)