Kick a player

Is that possible?

You can only kick players that have been inactive for at least 3 turns. It used to be instant, but many people abused it (kicking for absolutely no reason).
It's located in players menu (if you're game admin).

What about before the game starts for e.g RP? and someone is just not playing by rules etc

You can kick before the game starts too, as long as you are the game host. This can only be done once on the game screen (before starting) and not the game lobby; just go to the players list select the player and there is a button to kick.