Sphere of activity (5)
(Other definitions for field that I've seen before include "The ... (John B Keane)" , "Pasture or crop land" , "Area of farmland" , "Flodden?" , "Area for crops/livestock" .)
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">sphere of activity</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 arena that I've seen before include "where there's competition" , "Scene of combat" , "Ring for contest" , "Sporting enclosure" , "Wembley, for example" .)