Running shoe (7)
I believe the answer is:
trainer
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">running shoe</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for trainer that I've seen before include "Coach - one of a pair of shoes?" , "teacher" , "Casual shoe" , "one that helps runner perform" , "Plimsoll or sneaker" .)