on the fiddle meaning

• Involved in swindling
• 
  [British slang]
  on the fiddle
  Phrs. In the process of cheating, or defrauding. See 'fiddle'.
  

• fiddle:    Noun: fiddle  ...
• fiddle with:    Verb: fiddle with& ...
• as fit as a fiddle:     (informal) & ...

Examples

1. They also recalled his musical talent on the fiddle and other instruments.
2. They first performed as a quartet with Alicia Jo Rabins on the fiddle.
3. There's no word on the fiddle.
4. After returning to Scotland he virtually gave up dancing and concentrated on the fiddle.
5. Audra promptly assembled an album of 22 instrumental songs played by Ruby on the fiddle and guitar.