Sort of knot judge has to work round (7)
I believe the answer is:
trefoil
'sort of knot' is the definition.
(trefoil knot is a type of knot)
'judge has to work round' is the wordplay.
I cannot really see how this works, but
'judge' could be 'ref' and 'ref' is located in the answer.
'to' is found in the answer.
This explanation may well be incorrect...
(Other definitions for trefoil that I've seen before include "Three-lobed leaf" , "clover, possibly" , "Three-leaved plant, eg clover" , "Loftier (anag) -- clover-like plant" , "Plant with clover-like leaves" .)