On the title screen (screen with Piazza holding the bat), press R Button, A Button, Z Button, R Button, Right C, A Button, B Button. You'll hear a confirmation tone telling you the code was done correctly. Wait for about a minute for the demo to appear, then press the A Button to escape out of the demo. Let the game run through the banners (MLB, GT Interactive, etc.) and after the Devil's Thumb banner goes by, the credits will roll.