Perhaps Wimbledon grassy patch cut based on usage (6,3)
I believe the answer is:
common law
'perhaps wimbledon' is the definition.
I can't tell whether this definition defines the answer.
'grassy patch cut based on usage' is the wordplay.
'grassy patch' becomes 'lawn' (I've seen this before).
'cut' means to remove the last letter.
'based' is a charade indicator (letters next to each other) (in a down clue, some letters are based on others).
'on usage' becomes 'common' (I can't justify this - if you can you should believe this answer much more).
'lawn' with its last letter removed is 'law'.
'law' put after 'common' is 'COMMON-LAW'.
Can you help me to learn more?
(Another definition for common law that I've seen is " Body of legal rules based on custom and judicial precedent".)