>You walk your butt over there and pick the damn ball up.
commented 18 minutes ago by Kawaii Terlor
Alright enough of the jokes though let's get a little more serious. If a trainer throws a Pokéball especially to catch a Pokémon, the trainer will most likely walk over to it and pick it up or sent a Pokémon to retrieve it.
Although not all Pokémon Trainers throw their Pokeball's a good distance away when calling out a Pokémon, some will simply throw it up in the air and catch the ball after the Pokémon's release.
However I do know what you're getting at, how can you throw a Pokeball a good distance away one minute and then it be in your hand the next minute. Well it has been speculated the Pokeball has some sort of auto-return feature that brings it back to it's trainer after they send their Pokémon out. Of course this is just speculation as I'm not quite sure if it's been confirmed, but their have been incidents in the Anime where a trainer throws a Pokeball up in the air diagonally and then catches it on the return despite not moving and throwing it diagonally.
Of course you can theorise for yourself why the Pokeball is instantly in the trainer's hand when he/she releases his/her Pokémon. But one thing you have to bear in mind though is that Pokémon is actually intended for children despite most of their fans being of a older nature. Game Freak also aren't exactly known for their logic or being realistic for that matter.
But I guess if you don't want to believe any of those theories, I suppose it's possible that the Pokémon simply passes the Pokeball back to their trainer once they are released with their tail or paws etc.