Produce trousers left for rider perhaps (6)
I believe the answer is:
clause
'for rider perhaps' is the definition.
(rider is a kind of clause)
'produce trousers left' is the wordplay.
'produce' becomes 'cause' (produce can mean to cause or create).
'trousers' is an insertion indicator (trouser can mean to steal or take).
'left' becomes 'l' (common abbreviation).
'cause' going around 'l' is 'CLAUSE'.
(Other definitions for clause that I've seen before include "Proviso" , "Subdivision of a sentence" , "Separate section of a legal document" , "Section in a contract" , "Not quite a full sentence" .)