Warm up for a bout (4)
I believe the answer is:
spar
'warm up for a bout' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for spar that I've seen before include "Train at boxing; mineral" , "possibly rigged" , "Box (lightly) - fight (verbally)" , "bar" , "Fight (in training) - pole (on boat)" .)