Violent thug entering denial? That's bad (7)
I believe the answer is:
naughty
'bad' is the definition.
('naughty' can be similar in meaning to 'bad')
'violent thug entering denial?' is the wordplay.
'violent' indicates anagramming the letters.
'entering' indicates putting letters inside.
'denial?' becomes 'nay' (nay is a kind of denial).
'thug' anagrammed gives 'ught'.
'ught' placed into 'nay' is 'NAUGHTY'.
'that's' acts as a link.
(Other definitions for naughty that I've seen before include "Disobedient, child perhaps" , "Badly-behaved" , "Behaving badly or risque" , "Risqu" , "mildly indecent" .)