Here is the full list of all 9 Fireteam achievements.
Level up and reach Level 5
Level up and reach Level 10
Level up and reach Level 15
Level up and reach Level 20
Level up and reach Level 25
Won your first match
In a single match claim 10 death tags that weren't yours
In a single match claim 5 of your own death tags back before they are collected
In a single match claim 15 death tags that belong to you