A fight following one change of policy (5-4)
I believe the answer is:
about-face
'change of policy' is the definition.
'about face' can be an answer for 'change' (I have seen 'Change of attitude' mean 'about face' so perhaps 'change' could also mean 'about face'). I am not sure about the 'of policy' bit.
'a fight following one' is the wordplay.
'fight' becomes 'bout' (as in a bout in boxing).
'following' becomes 'f' (used when citing page numbers etc).
'one' becomes 'ace' (ace has a value of one in some card games).
'a'+'bout'+'f'+'ace'='ABOUT-FACE'
Can you help me to learn more?
(Another definition for about-face that I've seen is " Complete change of opinion or attitude".)