Leading sheep of a flock (10)
I believe the answer is:
bellwether
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">leading sheep of a flock</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 bellwether that I've seen before include "Leading sheep of a flock" , "Leader of the flock" , "Sheep that leads the flock -- we tell Herb (anag)" , "Leading sheep; trendsetter" .)