Run into battle (9)
I believe the answer is:
encounter
I believe this clue is a double definition.
'run into' is the first definition.
('encounter' can be a synonym of 'run into')
'battle' is the second definition.
(encounter is a kind of battle)
(Other definitions for encounter that I've seen before include "Meet, come across" , "battle" , "Struggle" , "Come upon, meet" , "See 19" .)