Let inside course of a casino game (8)
I believe the answer is:
roulette
'a casino game' is the definition.
(I've seen this in another clue)
'let inside course' is the wordplay.
'inside' means one lot of letters goes inside another.
'course' becomes 'route' (I've seen this before).
'let' put into 'route' is 'ROULETTE'.
'of' is the link.
(Other definitions for roulette that I've seen before include "Table game" , "gambling business" , "it's a gamble" , "Wheel for the gambler" , "Spinning-wheel game" .)