Joining up (9)
I believe the answer is:
enlisting
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">joining up</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for enlisting that I've seen before include "Joining up" , "Recruiting" .)