The OSC started doing 2 divisions this year, top teams that placed last year, were considered for the masters divisions, all others to the lower division, if you are new to OSC, you can start at Players div, which in my opinion is more fun, NSA, well I dont think there is ranking in NSA, but it sure is fun
OSC split the divisions, making a Master's and a Player's division, which seeds the top teams in the Master's and new teams in the players. If you play Master's division, you can not bump down without the other teams voting and giving an "ok". I believe the bottom 3 teams in Master's division for the season get brought down to Player's div, and the top 3 get bumped up.
NSA used to be an invite only league but as of this past season, it was opened up to anyone that wanted to play. There are no "divisions" per say, and it is an open tournament, meaning from rookie to pros, everyone is welcome to play.
The OSC is an awesome league to begin, because of the 3-man format. Always easier to build and maintain a team with less people, and the format lends itself to learning because there are less people to have to coordinate with, whereas in 5 and 7 man, in order to have a strong team, you MUST make moves that are coordinated and communicate between more people.