Playing the violin involved a bit of sharp practice (2,3,6)
I believe the answer is:
on the fiddle
'involved a bit of sharp practice' is the definition.
I know nothing about this answer so I cannot judge whether it can be defined by this definition.
'playing the violin' is the wordplay.
'playing' becomes 'on' (on can mean playing or performing).
'violin' becomes 'fiddle' (synonyms).
'on'+'the'+'fiddle'='ON THE FIDDLE'
Can you help me to learn more?
(Other definitions for on the fiddle that I've seen before include "Dishonest" , "Cheating (colloq.)" , "Involved in swindling" , "Engaged in cheating" , "leader of the orchestra?" .)