Trained Up Achievement
Win 10 multiplayer games while playing in Combat Training playlists.
Combat Training is a game mode where you fight bots. You can do this solo or with friends. The easiest way to get this is to make the enemy score limit as low as it will go and give the enemy team the most amount of members.
When in the multiplayer menu, you can select the combat training game mode. Play that game mode with friends or solo and after 10 victories you should get the achievement.
Note: Bootcamp playlist becomes unavailable at Sergeant (level 11). You will have to play Objective from then on if you wish to get the achievement.