On the title screen, hold B and press Start. You will access a hidden screen known as Ball Speed Mode. There, you can adjust the throwing distance (option 1) from 1-30 meters, pitch it (option 2) to start the spinning numbers, catch it (option 3) to see the speed, then reset to throw again (option 4). The max speed is recorded, so you can try and beat that score if you want. To exit this mode, you must turn off/on the game.