Review volunteer fighters once admitting death in hostile campaign (8)
I believe the answer is:
vendetta
'death in hostile campaign' is the definition.
The definition and answer can be both acts as well as being singular nouns.
Perhaps you can see an association between them that I can't see?
'review volunteer fighters once admitting' is the wordplay.
'review' becomes 'vet' (I've seen this in other clues).
'volunteer' becomes 'TA' (member of the Territorial Army, volunteer regiment).
'fighters once' becomes 'end' (I am not sure about this - if you are sure you should believe this answer much more).
'admitting' is an insertion indicator.
'vet'+'ta'='vetta'
'vetta' going around 'end' is 'VENDETTA'.
Can you help me to learn more?
(Other definitions for vendetta that I've seen before include "Murderous feud" , "Sicilian blood feud" , "Private feud" , "murderous campaign?" , "Prolonged bitter quarrel" .)