Practice boxing (4)
I believe the answer is:
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">practice boxing</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this in another clue)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for spar that I've seen before include "Box; various minerals" , "What boxers do" , "Sticks" , "bar" , "Box for practice" .)