Level, then winning -- prepare to fight (6,2)
I believe the answer is:
square up
'prepare to fight' is the definition.
(I've seen this before)
'level then winning' is the wordplay.
'level' becomes 'square' (I am not sure about this - if you are sure you should believe this answer much more).
'then' says to put letters next to each other.
'winning' becomes 'up' (eg being up at half time in football).
'square'+'up'='SQUARE UP'
Can you help me to learn more?
(Other definitions for square up that I've seen before include "Pay a debt" , "Settle" , "prepare to fight" .)