Loud order to start shooting in group (7)
I believe the answer is:
faction
'group' is the definition.
'loud order to start shooting' is the wordplay.
'loud' becomes 'f' (short for forte - 'loud' in music).
'order to start shooting' becomes 'action' (I've seen this before).
'f'+'action'='FACTION'
'in' acts as a link.
(Other definitions for faction that I've seen before include "Wing" , "Cabal" , "camp" , "Rebellious group" , "Act on if for a small group within a larger one" .)