It's a ball (6)
I believe the answer is:
sphere
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">it's a ball</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 sphere that I've seen before include "Ball or field of influence" , "Globe or domain" , "Orb or globe" , "Particular environment or walk of life" , "Round object" .)