Boxes, and gets involved in conflict on playing field (10)
I believe the answer is:
rectangles
'boxes' is the definition.
'gets involved in conflict on playing field' is the wordplay.
'gets involved in conflict' becomes 'tangles' (tangle can mean to get into a fight).
'on' is a charade indicator (letters next to each other).
'playing field' becomes 'rec' (short for recreation ground).
'tangles' put after 'rec' is 'RECTANGLES'.
'and' is the link.
(Other definitions for rectangles that I've seen before include "they may be squares" , "Four-sided figures" .)