Withdraw without taking part in fight (3,3)
I believe the answer is:
bow out
'withdraw' is the definition.
(I know that withdraw can be written as bow out)
'without taking part in fight' is the wordplay.
'without' becomes 'wo' (abbreviation of 'without', normally with a slash).
'taking part in' indicates putting letters inside.
'fight' becomes 'bout' (as in a bout in boxing).
'wo' going into 'bout' is 'BOW OUT'.
(Other definitions for bow out that I've seen before include "Withdraw from a situation" , "Retire from the scene with bodily gesture of acknowledgement?" , "Exit; retire" , "Retire gracefully" , "What a string player often gets" .)