Don't Be cRule - What is the Swiss System

 A Neutral Take Planning to Fight Wars, or, 

Poking Holes in a Popular Organizing Method

So, most WCC events are run using the “Swiss” System – what does that actually mean?  Believe it or not, there are 30 pages in the USCF Rulebook to answer that question – See Sections 27 and 28, that’s what I’m using to write this.  I won’t dive into all 30 pages, but I will explain the Why and the What in enough detail for you to be able to guess who you might play next week.

TL;DR for the Swiss System (putting these at the top of the post now…it’s OK, I’m the only one reading them anyways, lol)

• Swiss System lets more players stay involved longer in a multiple round event while better identifying a clear winner, knockout events cut the field on every round, round robins need more rounds to find a winner.
• Rounds are paired by score group, with top half (by rating) in that score group playing the bottom half.  Colors assigned to equalize over course of the event.

Why use the “Swiss” system?  Other sports don’t…

You’re right about that.  Many sports play a regular season and then have a knockout system for playoffs, while other sports organize “knockout” or bracket or match play events where winners advance and losers go home.   Almost all professional sports play some hybrid of these systems, why don’t we?  Well, club and weekend chess is a little different for at least two reasons:

• Not many of us would want to play in a 5-week club event - or even a 5-round weekend event – where we could lose in the first round and have nothing to do for the rest of the time.
• Not many of us would want to play a 20-person event organized as a 19 round “round robin” or “all-play-all” event.

So, if we want everyone to have fun for the whole event, and there are too many players to logistically manage a round-robin, we need a way to find a winner without worrying that some players had an easier path through the field than others.  If more games are competitive as a result, that’s a great side benefit as well.

So, these are the goals, and the reasons why knockout/bracket events or round-robins aren’t popular for club and weekend events.  The Swiss system is one common way to achieve these goals – let’s see how.

How does the Swiss System Work?

To use the Swiss System to find pairings for a round in an event we need two numbers for every player: 1) Their current score, and 2) Their current rating.  At the highest level, the rules are very simple:

1.  For every score group, list all of the players in order of their rating.
2. Cut this list exactly in half, a “top” half and a “bottom” half by rating
3. The highest rated player in the top half of the list plays the highest rated player in the bottom half of the list, and so on down the list.
4. For colors use the following guidelines
• In round 1, start with a random choice: highest rated player gets either White or Black, then alternate for each game in this round (if the higher rated player on board 1 gets Black, then the higher rated player on board 2 gets White, and so on…)
• For later rounds, pairings are set to prefer equalizing colors and to not have players assigned the same color more than twice in a row.

And that’s basically it.   Note that for the first round of an event, everyone’s score is 0, so this system works just fine there, too.  Why is this such a good system that it is nearly ubiquitous in club and weekend play??

• It assures that everyone in a score group has similar rating differences for their game, so there’s less of a complaint about one player’s “path” to their score being different than another’s.  
• For the first round in an event, the top player plays the player just below the middle by rating, and the 5^th from the top plays the player 5^th down from the middle.  These are likely to be similar rating gaps, so all 4 of these players – 2 from the top and 2 from the bottom of the list will have had a similar pairing.
• It does a good job (but not perfect) in identifying a clear winner.  An n round event can accommodate up to 2ⁿ players such that there is no more than 1 perfect score.  When we include the possibility of draws, typically twice this number of players can be reduced to no more than one perfect score.  For 32 players, this means a 5 round event is enough, certainly less than the 31 rounds for a Round-Robin event…  This scales quickly – in an event like the Chicago Open, the 9-Round Open section could accommodate 512 players, while the other sections (for us mortals) are 7 rounds which guarantees no more than 1 perfect score for 128 players in each section.
• It also means that most of the time after the first round or so, players are playing competitive games with players within a class or so of their rating.
• It also means that one bad round or result isn’t the end of your event.  “Playing a Swiss gambit” means an early draw or loss for a higher rated player, meaning they may have a slightly easier path in later rounds, and thereby still stay in contention.  In a knockout event, a bad result means the end of the event

I know there are exceptions: if there’s a group with an odd number of players, or two players have already played, or one would get 3 Blacks in a row, this doesn’t exactly work as written, but these guidelines are close enough to understand 95% of the pairings that actually get made.  If you’re interested, get a copy of the rule book, or ask a TD, or, if you’re really interested, tell a TD you’d like to help out and maybe become a TD !

Hope this is helpful

John D