Public protest (4)
I believe the answer is:
demo
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">public protest</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 demo that I've seen before include "Eg, protest march" , "exhibit" , "Protest (abbr)" , "presentation" , "Brass instrument valve" .)