Leave idler no change for boatman (9)
I believe the answer is:
gondolier
'for boatman' is the definition.
(gondolier is a kind of boatman)
'leave idler no change' is the wordplay.
'leave' becomes 'go' (to go is to depart or leave).
'change' is an anagram indicator.
'idler'+'no'='idlerno'
'idlerno' anagrammed gives 'ndolier'.
'go'+'ndolier'='GONDOLIER'
(Other definitions for gondolier that I've seen before include "Singular SO" , "Venetian waterman" , "to leave Red Lion disorientated" , "Propeller of Venetian boat" , "Punter" .)