Simple game: scrap a more difficult one (5)
I believe the answer is:
bingo
'simple game' is the definition.
(bingo is a game of luck)
'scrap a more difficult one' is the wordplay.
'scrap' becomes 'bin' (I've seen this in other clues).
'a more difficult one' becomes 'go' (I can't explain this - if you can you should believe this answer much more).
'bin'+'go'='BINGO'
(Other definitions for bingo that I've seen before include "Voila!" , "House!" , "I've completed my card!" , "Game of chance" , "Popular gambling game in which numbers are called at random" .)