This is earned by winning 10 games of any type in a row. (You can't lose a single game for at least 10 games.)
If you want to speed up the process and take the easy route, load up an Exhibition game with these settings:
Arena/Map: Any
Team Size: 1v1
Bot Difficulty: No Bots
Mutator Settings: Max Goal = 1
Now you can pick any team you want (it will only be you) and simply make a goal which will end the match immediately and count towards a win. Rinse and repeat this method 10 times for your achievement.
Here's a visual reference as to how easy and fast it is to create and finish an Exhibition map for this achievement: