Churchmen in moral transgression (8,3)
I believe the answer is:
cardinal sin
'churchmen' is the definition.
I don't know anything about this answer so I cannot tell whether this works.
'moral transgression' is the wordplay.
'moral' becomes 'cardinal' (I can't justify this - if you can you should believe this answer much more).
'transgression' becomes 'sin' (sin is a kind of transgression).
'cardinal'+'sin'='CARDINAL SIN'
'in' acts as a link.
Can you help me to learn more?
(Another definition for cardinal sin that I've seen is " fundamental foul-up".)