( I am a xbox 360 owner and missed the bus on this great free downloadable content)
Go to the Reebok website provided below, sign up and BAAM. you will be provided the code.
Here is the code that was given to me, F5KG-L2B8-G93G
I entered into the sweepstakes, Free Games, Autographed Jerseys etc.
http://www.reebok.com/US/afl
or
http://www.reebok.com/US/afl?source=cj
