Balding (4,2,3)
I believe the answer is:
thin on top
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">balding</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this in another clue)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for thin on top that I've seen before include "Balding (colloq.)" , "Result of losing hair, balding" , "not so hairy now" , "developing a shine for the Head?" , "with less than full head" .)