It may seem to make sense to use setup() for this kind of thing but that is incorrect. setup() should be used to set up the environment, connect to the displays, show a "hello" message and that kind of thing.
The main loop() should be used to ask the user a question, start and stop a game. What if you want a new game with a different number of players? It's difficult to go back to setup() at that point.
It also spreads your user-interface button code around the place. If you are forced to change one button to a different pin or some other trivial change, suddenly it's more difficult to find, change and test all of those different parts of the code.