The short explanation is that the Challenge Legaue is the qualifying tournament for the Duel Tournament, which itself is the qualifying tournament for the next Starleague. Everything culminates in the Starleague, where all the money is, but also where the players face the toughest competition on the planet.
But, that may be a bit too brief for some, so let me explain in more detail. Things start off with the Challenge League. There's a one-day qualifying tournament to get into the Challenge League itself involving 96 (or so) players. What's important is that only 24 players make it into the Challenge League. Those 24 are then divided into Groups of 4 (so, for the numerically CHALLENGED, that's 6 Groups, A - F, in total). Players within each Group do a double-elimination format mini-tournament. The top 2 players from each Group qualify for the Duel Tournament, so you have 11 Challenge Leaguers advancing into the Duel Tournament.
But, wait! If 2 players qualify from each Group and there are 6 Groups, isn't that 12 players who qualify for the Duel Tournament and not 11?! mensrea, are you D-U-M?! Well, I could be, but not in this case. You see (and this format began with the 2nd Challenge League in the middle months of 2002) the 6 qualifiers who make it out of their Challenge League Groups ranked #1 (i.e. the players who made it through the double-elim without a single loss) get to battle each other one final time to determine the "winner" of the Challenge League itself. The Challenge League winner gets an automatic seed in the next Starleague and does not need to play in the Duel Tournament. This guy is SET!
Ok, still with me? So what happens in the Duel Tournament? Well, basically, 13 players (i.e. all players who didn't make top 3) from the previous Starleague (which usually runs contemporaneously with the Challenge League and, after that's done, the Duel Tournament) get paired with the 11 Challenge Leaguers in another 24-person (13 + 11), 6-Group double-elim mini-tournament, only this time, there's no "winner:" the top 2 from each Group simply qualify for the next Starleague (which is what everyone's been playing their asses off for anyway). And that's it for the Duel Tournament!
But why 13 from the previous Starleague? Well, because OnGameNet, in a stroke of genius, decided that the top 3 finishers from the previous Starleague should get seeds in the next Starleague and not have to play in the Duel Tournament to qualify again. Remember: Starleague is a 16-person tournament divided into 4 deadly Groups A - D. So, the top 3 from the previous Starleague each get seeds at the top of different Groups in the next Starleague (so they don't have to play each other in the first round). The fourth and final Group seed in the Starleague, of course, goes to the winner of the Challenge League (remember?).
Overall, this current format is way cooler, especially because it means that the usually boring 3rd/4th place match in the Starleague now gets turned into a fiercely contested, no-holds-barred CATFIGHT, where the difference between 3rd (an automatic seed in the next Starleague) and 4th (down you go to do battle and face possible elimination in the Duel Tournament) is no longer just a matter of a few extra Korean Won and bragging rights.
Hope you got all that. 'Cause I ain't doing this again...
mensrea
2002. 11. 20