Work hard enclosing judge’s leafy plant (7)
I believe the answer is:
trefoil
'leafy plant' is the definition.
(I know that trefoil are often leafy)
'work hard enclosing judge's' is the wordplay.
'work hard' becomes 'toil' (to toil is to do strenuous work).
'enclosing' is an insertion indicator.
'judge' becomes 'ref' (referee).
'toil' going around 'ref' is 'TREFOIL'.
(Other definitions for trefoil that I've seen before include "Three-leaved plant, eg clover" , "Small clover-like plant" , "bacon-and-eggs?" , "Clover leaf" , "clover, possibly" .)