Get me a lawyer!
All games have some sort of rules - even if they are very basic or very fluid. Rules give a game the structure it needs so all players know what they need to do. Rules allow everyone to know what to expect from a game, even if the game includes a lot of randomness or unpredictability. Rules aim to prevent disagreements among players. Without rules there would probably be chaos - but then sometimes that is what you want from a game.