Breach of law over area that is disputed region (6)
I believe the answer is:
crimea
'is disputed region' is the definition.
(Crimea is a disputed territory)
'breach of law over area' is the wordplay.
'breach of law' becomes 'crime' (something against the law).
'over' is a charade indicator (letters next to each other) (in a down clue, some letters go over others).
'area' becomes 'a' (maths abbreviation).
'crime'+'a'='CRIMEA'
'that' acts as a link.
(Other definitions for crimea that I've seen before include "Ukrainian peninsula, scene of war" , "European peninsula" , "Where there was a battle" , "High-quality black tea" , "'Ukrainian peninsula, site of a 19th-century war (6)'" .)