I'd also like to add that Smogon is just one of a few different metagames that has its own set of tiers, rules, and regulations that it defines for itself. An example of another metagame is
VGC (Video Game Championships), which is the metagame officially sanctioned by Nintendo for its tournament battles. It has a few sets of rules that are completely different from Smogon's rules, and the play style is a lot different as a result. For example:
- All battles are in double battle format
- No two Pokémon can carry the same hold item, whereas with Smogon, this rule doesn't exist.
- There's no tiers--only mythical Pokémon are banned.
Smogon is of course the most accessible, but still keep in mind that there's not just one set of rules, there's actually several depending on the medium your battle is taking place on :)