Box in convenience store (4)
I believe the answer is:
spar
'box' is the definition.
(spar can mean to box)
I cannot understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for spar that I've seen before include "Fight - something probably rigged?" , "bar" , "Crystal - box" , "Box without punching hard" , "Rafter, boom" .)