Rider has reason to save pounds (6)
I believe the answer is:
clause
'rider' is the definition.
(I've seen this in another clue)
'reason to save pounds' is the wordplay.
'reason' becomes 'cause' (I've seen this in another clue).
'to save' is an insertion indicator.
'pounds' becomes 'L' (L can represent the monetary pound).
'cause' going around 'l' is 'CLAUSE'.
'has' is the link.
(Other definitions for clause that I've seen before include "Part of sentence or document" , "part of legal document" , "Separate section of a legal document" , "Section in a contract" , "Verb-carrying component of sentence" .)