Crime fast overwhelming Ireland (6)
I believe the answer is:
piracy
'crime' is the definition.
(piracy is a kind of crime)
'fast overwhelming ireland' is the wordplay.
'fast' becomes 'pacy' (I've seen this before).
'overwhelming' is an insertion indicator.
'ireland' becomes 'ir' (abbreviation for Ireland).
'pacy' going around 'ir' is 'PIRACY'.
(Other definitions for piracy that I've seen before include "Illegal copying" , "Copyright infringement" , "Buccaneering" , "Crime" , "Maritime or commercial robbery" .)