When you're catching a Pokémon, there is a coloured circle inside the white circle. This circle goes from green to yellow to red. I'm guessing this colour represents the difficulty of capturing that Pokémon because yellow-red Pokémon seem to break free a lot.
However that circle varies in size and goes from being overlaid over the white circle all the way down to tiny little circle I can barely see.
Here the green circle is at max size.
What does this size actually mean? Is it distance that your Pokéball was from the Pokémon or something else?
Best Answer
The ring and its colours are detailed in the official FAQ for Finding and Catching wild Pokémon.
The colour of the ring represents the catching difficulty of the pokémon.
The size of the ring represents your increased chance of catching the pokémon.