Pole to fight, but not seriously (4)
I believe the answer is:
spar
I believe this is a double definition.
'pole' is the first definition.
(I know that spar is a type of pole)
'fight but not seriously' is the second definition.
(I've seen this in another clue)
'to' is the link.
(Other definitions for spar that I've seen before include "Wooden pole -- box" , "Scrap" , "Box in training - nautical pole" , "Shadow box" , "Mineral; box; wing beam" .)