Game course allowed to be included (8)
I believe the answer is:
roulette
'game' is the definition.
(roulette is a kind of game)
'course allowed to be included' is the wordplay.
'course' becomes 'route' (I've seen this before).
'allowed' becomes 'let' (I've seen this before).
'to be included' means one lot of letters goes inside another.
'route' placed around 'let' is 'ROULETTE'.
(Other definitions for roulette that I've seen before include "Game of chance with small ball" , "French gambling" , "Gambling game with spinning wheel and ball" , "risky venture" , "Form of gambling" .)