Villainous foe ruins a broadcast (9)
I believe the answer is:
nefarious
'villainous' is the definition.
(I know that villainous can be written as nefarious)
'foe ruins a broadcast' is the wordplay.
'broadcast' indicates anagramming the letters (letters scattered or cast around).
'foe'+'ruins'+'a'='foeruinsa'
'foeruinsa' with letters rearranged gives 'NEFARIOUS'.
(Other definitions for nefarious that I've seen before include "immoral?" , "Wicked, criminal" , "Very bad" , "Villainous" , "Extremely wicked" .)