From Halopedia, the Halo wiki
The Procrastinator is an Achievement in Halo Wars that is unlocked when the player disrupts all tractor beams on Shield World.
It is worth 5 Gamerscore.
This achievement is quite easy, just send Gremlins to each of the tractor beams (preferably on easy).
They do not need combat support because they have relatively strong armor, and when one is positioned next to a beam, it will become immune to damage.