Make the first bet (4)
I believe the answer is:
open
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">make the first bet</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this in another clue)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for open that I've seen before include "Not yet decided - to start" , "Unenclosed" , "Frank - accessible" , "sporting competition" , "Contest that includes all comers" .)