One’s arresting oafish Aussie for contempt (7)
I believe the answer is:
mockery
'contempt' is the definition.
(thesaurus)
'one's arresting oafish aussie' is the wordplay.
'one's' becomes 'my' (both can mean belonging to the person writing).
'arresting' indicates putting letters inside.
'oafish aussie' becomes 'ocker' (I've seen this before).
'my' enclosing 'ocker' is 'MOCKERY'.
'for' is the link.
(Other definitions for mockery that I've seen before include "Derision" , "Travesty" , "Ridicule" .)