Dull discourse about card game in bar (9)
I believe the answer is:
proscribe
'bar' is the definition.
(thesaurus)
'dull discourse about card game' is the wordplay.
'dull discourse' becomes 'prose' (I can't explain this - if you can you should believe this answer much more).
'about' is an insertion indicator.
'card game' becomes 'crib' (crib is a kind of card game).
'prose' enclosing 'crib' is 'PROSCRIBE'.
'in' acts as a link.
Can you help me to learn more?
(Other definitions for proscribe that I've seen before include "Exile" , "Prohibit" , "Denounce" , "Ban" , "Forbid; condemn" .)