Anyone may open a tournament or cup. It can be a long lasting cup with big prizes, or no prizes at all, just for fun, or just a quick tournament that takes 1 day to play. You set your own rules, but they should be fair and reasonable for people to get interested. Once you've created something, make sure you advertise about it on other places. This is more of an advice if you want lots of players to sign up. Having prizes for the winners is also a big thumb up.
You may create 1-3 threads for each tourney/cup/league you open. No more.
All threads in this new board mustn't always include a tournament, cup or league. Maybe you want to ask questions like "Does anyone want to help me organize a new tournament for this game type...", or polls etc etc
I will also host another DM tournament very soon with more money involved!