When throwing a PokéBall at a Pokémon to capture it in Pokémon Go, you can increase your chances of catching it based on how well you throw. The white circle around the Pokémon determines the quality of your throw, and the one inside of it that is consistently shrinking determines the accuracy. If you throw your PokéBall inside of the shrinking circle, you can receive a Nice, Great, or an Excellent throw. Of the three, the Excellent throw is the most difficult to achieve.
To achieve an Excellent throw, you need to wait for the shrinking circle to nearly reach the dead center of the larger circle. It creates a small icon at the center of the Pokémon, making it pretty hard to hit dead-on. You can only achieve an Excellent throw by making your PokéBall throw land in the smaller circle, not by waiting for the smaller circle to appear and then attempting to capture the Pokémon.
An early strategy by some Pokémon Go trainers was to wait for the circle to become extremely small, and then take their finger off of their PokéBall. Unfortunately, you can’t do that anymore, and it resets it.
When the icon becomes smaller enough, you throw you PokéBall at the one in front of you and hope it hits the icon. You will know if it hit the smaller one because it will have a notification and tell you if it was a Nice, Great, or an Excellent Throw. You will likely switch between it being a Great or Excellent throw, especially when you attempt to wait for it to become smaller.
A great way to rack up Excellent Throws is to do it on more common Pokémon, such as those you encounter while walking around or hanging new PokéStops. It’s much more challenging to have it happen against Legendary Pokémon and research task encounters. When you land the Excellent throw, it increases the chances you catching that Pokémon.
It takes quite a bit of practice to nail an Excellent Throw. Because of how small the inner icon needs to be, it won’t be easy, and you probably don’t want to try and go for when the target Pokémon is far away. Try to wait until you encounter a Pokémon that’s pretty close to you.