Every video game needs to be defined by a set of rules. Both the design team and the player need to know exactly what is being represented in the game, what are the abilities, challenges and goals?
Lets say we are making a racing game. Will it be on a linear track (Gran Turismo), a track with multiple routes (Motorstorm), or a completely open world where the player chooses their own route (Burnout Paradise)? What real world phyics do we wish to simulate? Gravity obviously, but what about wind resistance, different track surfaces, weather conditions? Should the car suffer no damage at all, cosmetic damage only, or be completely destroyed in a crash? Is the player trying to win the race (Mario Kart), score the most points (Project Gotham Racing) or destroy as many enemy cars as possible (F Zero X)?
Clearly there are a massive amount of rules to set out the boundaries of the game. But are they necessary? Just imagine our racing game with no rules. The player could go anywhere, at any speed, for no purpose or reward. What would be the point? When we play a game, we make a type of pact with the developer: “I will accept your rules, so long as they appear clear and fair to me, and attempt to play the game you have made for the rewards you have defined”. This is why millions of people will play a racing game like Forza, where a single serious crash can ruin an entire 10 minute race. They accept that this game has rules attempting to simulate reality, along the lines of “IF serious crash, THEN engine breaks”. Whereas millions more play racing games like Mario Kart, where its an intentionally outlandish ruleset, more like “IF serious crash, THEN play wacky sound effect”.
Two very different rule sets!
As I’ve said before, the rules of a game need to be straightforward and well explained to the player. A set of arcane rules will frustrate players. For example, a rule that a players car will degrade over time and need to be repaired would be hugely irritating, if not explained at the start. The players car would just be getting slower and slower, the player having no idea why. The rules also need to be, or at least appear to be, fair. If Car A is fast but weak, while Car B is fast but also strong, the player will not be happy. Why should one car have a strength and weakness, while another car has two strengths and no weaknesses? Finally, rules don’t always NEED to, but should at least try to appear sensible in the context of the games world and story. Looking at today’s FPS games, most of them have regenerating health. Makes perfect sense in Halo, where you are equipped with an energy shield that recharges. Makes very little sense in Call Of Duty, where you are just randomly healing bullet wounds. Its not a massive issue really, but one that should not be ignored either.
In addition to the developer’s rules, players will often (sometimes unconsciously) implemement their own “gentleman’s”, or “common sense” rules. For example, in a turn based game such as chess, there may be no formal time limit to a players move. But after a minute or two, most people will say “You’ve had enough time, come on!”. Or in an FPS, camping (hiding in one spot for the entire game) is usually looked down on despite being allowed by the games rules. We all know that one friend who will argue “It’s allowed!” despite the entire room calling him a poor sport. Needless to say, that friend won’t be played with again.
Related to poor sportsmanship is outright cheating. This a lot more serious, and involves outright breaking the game, hacking it, or exploiting unintentional loopholes. For example, in Call Of Duty there was a trick to select a rocket launcher in such a way that upon death, the cheating player’s body would cause a massive explosion, generally killing loads of the enemy. This was a glitch that was since fixed, but loads of people used it gladly until it was. While a poor sport will generally be looked down on or mocked, a cheater usually attracts savage hate from normal gamers. Using cowardly tactics is annoying, actively breaking the game to give yourself an advantage is just plain wrong.
From all this, it is clear that a games rules need to be carefully laid out and tested for problems and imbalance. A single (perceived or real) unfair rule can sink an otherwise perfectly good game.