Outsider (8)
I believe the answer is:
underdog
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">outsider</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 underdog that I've seen before include "Competitor expected to lose" , "Likely loser" , "Lower-rated competitor" , "certainly not a favourite!" , "Grounded (anag)" .)