Defiant bluster undermining cleric at broadcast (12)
I believe the answer is:
recalcitrant
'defiant' is the definition.
('recalcitrant' can be similar in meaning to 'defiant')
'bluster undermining cleric at broadcast' is the wordplay.
'bluster' becomes 'rant'.
'undermining' is a charade indicator (letters next to each other).
'broadcast' indicates anagramming the letters.
'cleric'+'at'='clericat'
'clericat' anagrammed gives 'recalcit'.
'rant' after 'recalcit' is 'RECALCITRANT'.
(Other definitions for recalcitrant that I've seen before include "Defiant" , "Obstinate in opposition" , "Obstinately disobedient - cartel in cart (anag)" , "Wilfully disobedient" , "Refractory" .)