Middle-distance runner (5)
I believe the answer is:
miler
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">middle-distance runner</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this in another clue)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for miler that I've seen before include "Athlete running 1,760 yards" , "Runner over a specific distance" , "Pre-metric middle-distance runner" , "horse" , "one who competes in the long run" .)