Failure of the mafia's corrupt insiders (6)
I believe the answer is:
fiasco
'failure' is the definition.
(a fiasco is a failure or disaster)
'of the mafia's corrupt insiders' is the wordplay.
'of' says the answer is hidden in the clue.
'FIASCO' is hidden in the letters of 'mafias corrupt insiders'.
(Other definitions for fiasco that I've seen before include "An absolute mess, what a farce" , "Humiliating disaster" , "washout" , "A debacle, complete mess" , "Sudden total disaster" .)