Customer’s legal right protected by court (6)
I believe the answer is:
client
'customer's' is the definition.
(synonyms)
'legal right protected by court' is the wordplay.
'legal right' becomes 'lien' (legal term).
'protected by' means one lot of letters goes inside another.
'court' becomes 'ct' (abbreviation used in road names).
'lien' going into 'ct' is 'CLIENT'.
(Other definitions for client that I've seen before include "Customer - dependant" , "Employer of professional" , "Dependant, hanger-on" , "Person represented by lawyer" , "(Barrister's, social services') customer" .)