Something done after championship with legal document (5,4)
I believe the answer is:
title deed
'legal document' is the definition.
(title deed is a kind of legal document)
'something done after championship' is the wordplay.
'something done' becomes 'deed' (I've seen this before).
'after' is a charade indicator (letters next to each other).
'championship' becomes 'title' (a championship is a sporting title).
'deed' put after 'title' is 'TITLE-DEED'.
'with' is the link.
(Other definitions for title deed that I've seen before include "Document giving legal right of ownership" , "Document establishing legal right to property" , "Having proof of ownership" , "Document proving ownership" , "Deleted it (anag.)" .)