Scam banking run for one on the fiddle (6)
I believe the answer is:
string
'one on the fiddle' is the definition.
(a fiddle or violin has strings on it)
'scam banking run' is the wordplay.
'scam' becomes 'sting' (sting can mean a scam or deceptive scheme).
'banking' is an insertion indicator.
'run' becomes 'r' (cricket abbreviation).
'sting' placed around 'r' is 'STRING'.
'for' acts as a link.
(Other definitions for string that I've seen before include "Series of events" , "This vest is made of large mesh" , "Violin wire" , "Row" , "Thin length of cord etc" .)