Threaten to stop supporting young offender (6)
I believe the answer is:
impend
'threaten' is the definition.
(thesaurus)
'stop supporting young offender' is the wordplay.
'stop' becomes 'end' ('end' can be a synonym of 'stop').
'supporting' is a charade indicator (letters next to each other) (in a down clue, some letters go below others).
'young offender' becomes 'imp' (I've seen this in other clues).
'end' after 'imp' is 'IMPEND'.
'to' is the link.
(Other definitions for impend that I've seen before include "Be about to take place" , "seen to be around the corner" , "(Of a bad thing) loom" , "Become imminent" , "menace" .)