Here is the full list of all 18 The Undisputables : Online Multiplayer Shooter achievements.
Earned when you achieve grade 1
Earned when you achieve grade 2
Earned when you achieve grade 3
Earned when you achieve grade 4
Earned when you achieve grade 5
Earned when you achieve grade 6
Earned when you achieve grade 7
Earned when you achieve grade 8
Earned when you achieve grade 9
Earned when you achieve grade 10
Earned when you achieve grade 11
Earned when you achieve grade 12
Earned when you achieve grade 13
Earned when you achieve grade 14
Earned when you achieve grade 15
Earned when you achieve grade 16
Earned when you achieve grade 17
Earned when you achieve grade 18