Marijuana underlying dodgy things in entertainment venue (9)
I believe the answer is:
nightspot
'entertainment venue' is the definition.
(I know that nightspot is a type of entertainment venue)
'marijuana underlying dodgy things' is the wordplay.
'marijuana' becomes 'pot' (slang term for marijuana).
'underlying' says to put letters next to each other (in a down clue, some letters lie under others).
'dodgy' is an anagram indicator (a dodgy or wrong order of the letters).
'things' with letters rearranged gives 'nights'.
'pot' put after 'nights' is 'NIGHTSPOT'.
'in' is the link.
(Other definitions for nightspot that I've seen before include "club, perhaps" , "venue providing entertainment" , "Club, disco" , "Place for after-dark entertainment" .)