Change after a boxing match, as soldiers may be ordered (5,4)
I believe the answer is:
about turn
'as soldiers may be ordered' is the definition.
(soldiers may be ordered to about-turn)
'change after a boxing match' is the wordplay.
'change' becomes 'turn' (turn is a kind of change).
'after' says to put letters next to each other.
'boxing match' becomes 'bout' (I've seen this before).
'a'+'bout'='about'
'turn' after 'about' is 'ABOUT-TURN'.
(Other definitions for about turn that I've seen before include "Contrary progression" , "Total change of direction" , "Pivot 180 degress" , "Volte-face" , "Reversal of direction" .)