Duke, as before, comes to court (4)
I believe the answer is:
quad
'to court' is the definition.
(quad can mean a rectangular courtyard)
'duke as before' is the wordplay.
'duke' becomes 'd' (abbreviation).
'as' becomes 'qua' ('qua' is a Latin term meaning 'in the capacity of').
'before' is a charade indicator (letters next to each other).
'd' after 'qua' is 'QUAD'.
'comes' is the link.
(Other definitions for quad that I've seen before include "One of four offspring at the same birth (abbr)" , "bike: > one of four" , "yard" , "Square (abbr)" , "One of four children born at one birth" .)