A friend asked me today "How do I begin to make a competitive Pokemon team?" so I told him "Have you decided on a lead yet?" and he just looked me blank in the face as if I was speaking in another language. So this post will be all about roles in Pokemon.
Each Pokemon fits a role in battling, some are best at attacking, some defending etc. This post will just cover the basics and I'll go further into depth later down the line. So an average team usually consists of these Pokemon.
A lead Pokemon as the name suggests is a Pokemon who's duty it is to start off the Pokemon battle. Leads usually carry Stealth Rocks (a move I'll go into at a later date) and are primarily used to scare off the opposing Pokemon forcing a switch. In doing so, you have a number of options if you can predict the switch such as stat enhancing, stealth rocks, pursuit etc.
Essentially a Pokemon with a high base Attack and wide physical movepool. Physical sweepers usually carry a type combination that negates common types of phsical attacks. By nature, they usually arent the fastest of Pokemon but they can deal a heavy hit to the opponent and if you manage to set up one them they can more often than not sweep the enemy team hence the name.
A Pokémon with high Special attack power and a special movepool wide enough to hit most opposing Pokémon effectively. Unlike physcal sweepers, special sweepers are fast (though there are exceptions), however the downside is they cannot hit as hard as physical sweepers as most Pokemon in this category has not got an extremely high special attack stat unlike their physical counterparts.
A Pokémon with high Defense, and usually a typing that resists common types of physical attacks, with a movepool that includes moves such as ones that recover HP, stall, etc. Most Physical Walls aren't fast, but Speed isn't something they need, anyway. Since Physical Sweepers can be so powerful and can defeat teams that aren't prepared, Physical Walls exist to stop them and absorb their attacks so the other Pokémon on their team don't have to take heavy damage, or waste EVs on Defense.
A Pokémon who can absorb damage from Special moves. This role can't be as easily compared to Physical Walls as Special Sweepers are compared to Physical Sweepers, as Special attacks aren't as common as Physical attacks.
A Baton Passer Pokémon, usually works best in a Baton Passing Team. Baton Pass permits Pokémon to pass on added effects to their allies such as those of Calm Mind, Cosmic Power and even Mean Look. A Baton Passer usually has one or more moves or abilities to boost his stats. The types and EV administration can vary very much, but it is generally preferred to have good Defenses and Hit Points. Umbreon and Ninjask make excellent Baton Passers
There are many, many more roles in Pokemon of which I'll go into at a later date and also Pokemon can fit more than one type of role though they're usually better at certain ones and its wise to play to their individual strengths.