Bloodless revolution for agents capturing base (7)
I believe the answer is:
anaemic
'bloodless' is the definition.
(I've seen this before)
'revolution for agents capturing base' is the wordplay.
'revolution for' says the letters should be written in reverse.
'agents' becomes 'CIA' (Central Intelligence Agency).
'capturing' means one lot of letters goes inside another.
'base' becomes 'mean' (synonyms).
'cia' enclosing 'mean' is 'cimeana'.
'cimeana' back-to-front is 'ANAEMIC'.
(Other definitions for anaemic that I've seen before include "uninspiring" , "bloody poor" , "strangely pale" , "Bloodless, sickly" , "Pallid, lacking vigour or colour" .)