There is the CWB (Clan War Belt) and the CWC (Clan Wars Contest) as well as the 1v1 Ladder.

All of those are essentially "leagues" or "perpetual tournies" with different rules for determining who fights whom.

History shows it is very difficult to sustain a league over any period of time-- especially if it is a 1v1 league. At first nobody wants to join (because they think it is another flash in the pan), then they FLOOD in, and then almost as quickly they lose interest. The number of "disappearing" players is really incredible.

So if you are going to have a league you might consider having a specific # of players to keep it manageable.

Go look at www.myleague.com as CBR says-- lots of good stuff there.