Act frivolously in military room before a fight (4,5)
I believe the answer is:
mess about
'act frivolously in military room before a fight' is the definition.
I can't judge whether this defines the answer.
'room before a fight' is the wordplay.
'room' becomes 'mess' (mess is a kind of room).
'before' is a charade indicator (letters next to each other).
'fight' becomes 'bout' (as in a bout in boxing).
'mess'+'a'+'bout'='MESS ABOUT'
Can you help me to learn more?
(Other definitions for mess about that I've seen before include "Act foolishly" , "Behave in a silly way" , "Behave foolishly" , "Potter around" .)