Defiantly aggressive criminal culture Unite oddly dismissed (9)
I believe the answer is:
truculent
'defiantly aggressive' is the definition.
(I've seen this before)
'criminal culture unite oddly dismissed' is the wordplay.
'criminal' indicates anagramming the letters.
'oddly dismissed' indicates alternate letters (odd-numbered letters get removed).
The alternate letters of 'unite' are 'nt'.
'culture' anagrammed gives 'trucule'.
'trucule'+'nt'='TRUCULENT'
(Other definitions for truculent that I've seen before include "Obstreperous" , "Defiant, rude" , "Quarrelsome" , "Aggressively defiant" , "Defiantly aggressive" .)