Inexperienced in retreat in combat (3)
I believe the answer is:
war
'combat' is the definition.
(I've seen this in another clue)
'inexperienced in retreat' is the wordplay.
'inexperienced' becomes 'raw' (similar in meaning).
'in retreat' is a reversal indicator.
'raw' back-to-front is 'WAR'.
'in' acts as a link.
(Other definitions for war that I've seen before include "Hostile situation" , "Combat" , "Fight" , "Battle" , "State of armed conflict" .)