With patch 1.6.1 Awesomenauts introduced Leagues!
These are subdivisions in the leaderboards where people with similar skilllevels are paired into their own League. There are 9 different Leagues ranging from 9 (Copper) as the lowest to 1 (Awesomantium) being the highest.
As you move up through the Leagues, the playergroups you are paired with get smaller and more elite, leaving only a handful of the best to be worthy of Awesomantium!
You can check your current League in the main menu, the leaderboards or the in-game scoreboard.