Force going with battle group (7)
I believe the answer is:
faction
'group' is the definition.
'force going with battle' is the wordplay.
'force' becomes 'F' (symbol used in Physics e.g. f=ma).
'going with' is a charade indicator (letters next to each other).
'battle' becomes 'action' (military action).
'f'+'action'='FACTION'
(Other definitions for faction that I've seen before include "Rebellious group" , "band" , "Dissenting group within a larger one" , "Wing" , "part of party" .)