Search volunteers coming back into battle (6)
I believe the answer is:
combat
'battle' is the definition.
('combat' can be a synonym of 'battle')
'search volunteers coming back' is the wordplay.
'search' becomes 'comb' (combing is a kind of searching).
'volunteers' becomes 'ta' (abbreviation for Territorial Army).
'coming back' is a reversal indicator.
'ta' in reverse letter order is 'at'.
'comb'+'at'='COMBAT'
'into' acts as a link.
(Other definitions for combat that I've seen before include "A fight or contest, sometimes mortal" , "Battle, warfare" , "Oppose" , "Fight - strive against" , "Battle or fight" .)