Tailback (5)
I believe the answer is:
queue
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">tailback</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 queue that I've seen before include "Line of waiters" , "Pigtail; get in line" , "Line of people waiting for something" , "orderly people?" , "Very British assembly" .)