Here is the full list of all 10 Kinect Sports Gems: Ping Pong achievements worth 50 gamerscore.
Reach level 1 (or observe another player doing so) to gain the rank of Spectator.
Reach level 2 (or observe another player doing so) to gain the rank of The Ponger.
Reach level 3 (or observe another player doing so) to gain the rank of Amateur Acer.
Reach level 4 (or observe another player doing so) to gain the rank of Top Spinner.
Reach level 5 (or observe another player doing so) to gain the rank of Net Vet.
Reach level 6 (or observe another player doing so) to gain the rank of Rally Master.
Reach level 7 (or observe another player doing so) to gain the rank of Paddle Prodigy.
Reach level 8 (or observe another player doing so) to gain the rank of The Natural.
Reach level 9 (or observe another player doing so) to gain the rank of Super Smasher.
Reach level 10 (or observe another player doing so) to gain the rank of King Pong.