Kinect Sports Rivals

The achievement description is a little confusing. What you need to do, from the main "island menu", go to My Game. Then select Friends List. From there select a friend that is highlighted (I used my girlfriend's account that was loaded on the same One, if you don't have a friend with the game perhaps you can use another account on just add my GT: Antares Maximus). Now select any of the "Vs Rival" activities along the top. You need to play and finish the activity for the achievement to pop.