Practice punches (4)
I believe the answer is:
spar
'practice punches' 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 "Pole-shaped part of the rigging" , "Mineral; box; wing beam" , "Box in training - mineral" , "Pole used in rigging - fight" , "Pole to support sails, rigging etc" .)