Battle affected gain unfortunately (8)
I believe the answer is:
campaign
'battle' is the definition.
(I've seen this before)
'affected gain unfortunately' is the wordplay.
'affected' becomes 'camp' (camp can mean exaggerated or affected).
'unfortunately' indicates anagramming the letters (a bad or unfortunate spelling).
'gain' with letters rearranged gives 'aign'.
'camp'+'aign'='CAMPAIGN'
(Other definitions for campaign that I've seen before include "Electioneer" , "Co-ordinated course of action" , "Series of activities to attain a goal" , "In election period" , "battle" .)