When Availible: Chapters 1, 2, 3, and 5
Objective: A new game is all the rage amoung the blitzball-bereft citizens in Luca. Mathematical skills and a quick mind are what is needed to beat the Sphere Break players at their favorite game. Collect coins while diigging in the Bikanel Desert or win them in matches. Come back to Luca during Chapter 3 to participate in the Sphere Break Tournament and see if you can defeat Shinra in the final match for the Lady Luck Dressphere.
Sphere Break is one of the few mini games that spans almost the entirety of the game. To start it, visit Luca after you see the Behind the Scenes mission explaining what Yuna was doing while Rikku and Paine were catching Leblanc at the concert. Head over to the blitzball stadium and go into the locker room on the right. There you'll meet up with Rin, the creator of Sphere Break. He'll give you some of the basics and refer you to a proctor in the other locker room.
Talk to Rin's beaked assistant to get 20 entry coins and the rules of the game. During Chapter 1, you can only play against this character, so take advantage of this time to get familiar with the game and win some more coins.
The number of players you can take on increases as you proceed through the game. In Chapter 3, head back to Luca for the Sphere Break Tournament. In Chapter 5, look in the locker rooms for even stronger players and greater challenges.