Box holding Eastern weapon (5)
I believe the answer is:
spear
'weapon' is the definition.
(I know that spear is a type of weapon)
'box holding eastern' is the wordplay.
'box' becomes 'spar' (spar can mean to box).
'holding' is an insertion indicator.
'eastern' becomes 'e'.
'spar' placed around 'e' is 'SPEAR'.
(Other definitions for spear that I've seen before include "pierce with this?" , "Shafted weapon for throwing or thrusting" , "Javelin or harpoon" , "Asparagus shoot" , "stick" .)