I don't know for sure what they are planning for the fall league, but I can tell you the format for the league that just finished, and I bet this upcoming league should be failry similar.
5 Man teams, semi-auto only capped at 15 bps, chrono at 285 fps, each game has a max of 10 minutes. One team starts behind the fort, the other team starts in the woods, and each side has a flag (stationary only, have to keep a live player near it to capture it) that they are protecting. I don't remember exactly what the point structure was, but you get X points for each player eliminated on the other team, a big bonus if you capture and hold the other teams flag at the end of the game, and Y points for winning the match if you a) capture the flag or b) have more live players at the end of the game.
I thought going into the league that there would be an advantage to starting in the fort side, but after playing all the way through the league, I don't believe that is the case any more. The woods side was much easier to set up an ambush in, and therefore was actually probably easier to defend, and there is an open area between the woods and fort that really equals out the difficulties of attacking from either side.
It was alot of fun, looking forward to the next season.