Small, standard box? (4)
I believe the answer is:
spar
'box?' is the definition.
(spar can mean to box)
'small standard' is the wordplay.
'small' becomes 's' (abbreviation - e.g. clothes size).
'standard' becomes 'par' (standard of play in golf).
's'+'par'='SPAR'
(Other definitions for spar that I've seen before include "piece of wood?" , "Pole to support sails, rigging etc" , "Pole used in boat etc - box" , "Crystal - box" , "Raps with large timber" .)