Independent army keeping quiet, not taking sides (9)
I believe the answer is:
impartial
'not taking sides' is the definition.
(I've seen this before)
'independent army keeping quiet' is the wordplay.
'independent' becomes 'i'.
'army' becomes 'martial'.
'keeping' means one lot of letters goes inside another.
'quiet' becomes 'p' (music symbol for 'piano').
'martial' going around 'p' is 'mpartial'.
'i'+'mpartial'='IMPARTIAL'
(Other definitions for impartial that I've seen before include "Objective" , "Disinterested" , "Treating all rivals equally" , "Showing lack of favouritism" , "not taking sides" .)