Denial admitting good person is obscene (5)
I believe the answer is:
nasty
'obscene' is the definition.
(I've seen this before)
'denial admitting good person' is the wordplay.
'denial' becomes 'nay' (nay is a kind of denial).
'admitting' indicates putting letters inside (admit can mean to welcome in or accept).
'good person' becomes 'st' (saint).
'nay' placed around 'st' is 'NASTY'.
'is' acts as a link.
(Other definitions for nasty that I've seen before include "Highly repugnant" , "Awful" , "Evil" , "Disagreeable" , "Mean" .)