What is a Poké Ball?
A Poké Ball is a device used to capture and transport Pokémon and is primarily carried by Pokémon Trainers. They provide a means for trainers to take their Pokémon anywhere with them even if the Pokémon would normally be too large or inappropriate. Along with transportation and storage, a trainers Poké Balls are directly linked to their Pokédex, allowing it to provide real-time feedback on important aspects of the Pokémon including its current condition, combat statistics, a list of known moves, and other more mundane information such as height, weight, and gender.
When attempting to capture a Pokémon the trainer must first hit it with the Poké Ball, and if the Pokémons vital signs are still intact (it is not fainted, or dead) it’s form becomes pure energy and contained inside the Poké Ball. If a Pokémon is attempting to resist capture, it does have a chance to break free from the Poké Ball, damaging the ball and making it unusable until repaired, but this becomes less likely the more exhausted or injured a wild Pokémon is, which is why it is common practice to battle and weaken a wild Pokémon before attempting capture. As most Pokémon will resist capture, it is imperative that a trainer battle the wild Pokémon to prove they are a worthy trainer. Pokémon caught in a way they may view as undesirable or unfair tend to be of lower loyalty and will be disobedient until the trainer proves themselves to the Pokémon.
Once captured, a wild Pokémon is assigned a league ID based on the trainer that captured it and tied directly to that trainers ID until it is traded, released, or given to another trainer by transferring the ID it is registered to. In order for trainers to differentiate at a glance, a transparent image of the Pokémon contained inside a ball is displayed on the outside of it that is created using the energized Pokémon inside.