How do I play an online multiplayer match using Game Center in Sonic & SEGA All-Stars Racing?
You must be signed into Game Center (for details on how to do this, please see the Getting Started section in the ReadMe).
From the Select Mode menu, select Multiplayer.
Select Game Center, then follow the on-screen instructions.
The Select Racer menu will appear once you are connected to a match. Select a racer.
Once a minimum of two players have connected to a match, the host (the first player to connect) can press the Enter (↵) key to begin the match.