Oh well, that`s a little bit complicated.
First, you have to create the thread code (don`t post it!).
Then you have to get the permission of a moderator to post your thread in the battle stadium,
And ta-daaa! You`ve got your league!
But it would be better if you don`t make one.
Cause there are enough leagues here and if you set up your league, nobody might visit it...