Practise boxing (4)
I believe the answer is:
spar
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">practise boxing</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for spar that I've seen before include "Pole-shaped part of the rigging" , "quarrel" , "Act as boxer" , "bar" , "Stout pole to support rigging" .)