Engage as a participant (7)
I believe the answer is:
involve
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">engage as a participant</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 involve that I've seen before include "Cause participation of (someone)" , "Implicate or be bound up with" , "Include as a part or result" , "Cause to share in" , "Entail" .)