After spring, run and box (4)
I believe the answer is:
spar
'box' is the definition.
(sparring is a kind of boxing)
'after spring run' is the wordplay.
'after' says to put letters next to each other.
'spring' becomes 'spa' (I've seen this before).
'run' becomes 'r' (cricket abbreviation).
'spa' put next to 'r' is 'SPAR'.
'and' is the link.
(Other definitions for spar that I've seen before include "Wooden pole -- box" , "Scrap" , "Crystal - box" , "have an argument without marked hostility" , "Box - mineral - rod" .)