To get this achievement there are 2 methods depending on what online achievements you already have.
Method 1- If you are new at this and have no online achievements, well this will make your life easy: follow the guide to get the medals for Elimination, Team Elimination and Post Grab, then when you are going for your fugitive medals follow this method:- Start a game with a friend, on Pirate Fortress, rifles as the default weapon. From the start, the player who is going to win captures a data post while the other player commits suicide using grenades (now in some instances this will end the battle and you will recieve 4000+ exp). Repeat again until the battle ends, getting you anywhere from 3900 exp to 4300 exp. This method should take around 12 hours to get the whole online component of the game complete.
Method 2- If you have all the online achievements and are already above level 10, follow the above method for winning at fugitive; your level will increase quickly, when you hit level 30 it will take 4-6 games like this to level up all the way to 40 so it is about 30-120 seconds per game. Once you hit level 40 it will take 6-10 games per level, so level 30 to level 50 will take around 1hour 30 mins - 2 hours per player.