Stratagem required when reporting offence (7)
I believe the answer is:
sleight
'stratagem' is the definition.
(thesaurus)
'reporting offence' is the wordplay.
'reporting' shows a homophone (sound like) (as it might sound when reported or spoken).
'offence' becomes 'slight' (slight is a kind of offence).
'slight' sounds like 'SLEIGHT'.
'required when' is the link.
(Other definitions for sleight that I've seen before include "Dexterity (usually of hand)" , "It's deceiving to the eye" , "Handy skill" , "Tricky cunning" , "Artful trick" .)