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How a Typical Go Tournament Works

The McMahon draw system

The way most go tournaments are organised is called the McMahon System. This is a bit like the Swiss system which I had better explain first.

In the Swiss system everyone starts on zero points. In each round you are drawn (randomly or in some seeded manner) against someone on the same number of points as you. Every time you win a game you get a point. If you have exactly 2^n people in a tournament and n rounds then it turns out that the overall winner is decided by a straight knock out. But the point of the Swiss system is that everyone gets to play in every round.

The Swiss system was invented for things like chess tournaments. In chess there is no handicapping system and so players are quite used to unevenly match games. However in go the grading system is well established. Most players know their kyu or dan grade and because of the handicapping system people are used to closely matched games. The McMahon system is a modification of the Swiss system designed specially for go.

In the, instead of everyone starting on 0 points, you start at a level equal to your dan grade minus 1. I.e. a player whose grade is 14 kyu would start on a McMahon score of -14 and a 3 dan would start on a McMahon score of 2. Then you play games against people on the same McMahon score as yourself and every time you win a game your McMahon score is increased by 1.

This is all very well, and ensures that everyone plays games against people of about their ability but it does not really produce an overall winner. To get round this you introduce a bar at some level. For example in the 1997 Bar-Low tournament the bar was at 5 kyu. This means that everyone with a grade of 5 kyu, 4 kyu, ... 1 kyu starts off at a McMahon score of -5. This means that they all have an equal chance of finishing up with the the lowest McMahon score and hence being declared the overall winner. In other words the top part of the draw has been turned back into a Swiss system.

Anyway in a McMahon tournament prizes are normally given out for winning some proportion of the games you play at your own level, say 4/5, so that everyone has a chance of winning something.

It might be argued that introducing a bar is a little bit unfair. In the example of the 1997 Bar-Low tournament it means that the 5 kyus have to play on equal terms with the 1 kyus. Whether this is fair or not depends on what the aim is. Without the bar there is absolutely no way that a 5 kyu could be the overall winner, however the 5 kyu had a fair chance of winning 4/5 games and getting a prize. However with the bar a 5 kyu has a chance (all be it a small one) of winning the tournament outright. Having a bar is also slightly unfair on people just below the bar. Suppose that a 1 kyu lost their first game. They would then be on a McMahon score of -5 and it would be perfectly reasonable to draw them against a 6 kyu who had won their first game.

(For those of you who are starting to feel sorry for the 5 kyus in the 1997 Bar-Low Tournament please rest assured. There was only one 5 kyu in the tournament and no 6 kyus. The 5 kyu was given a free choice and chose to be above the bar.)

It is also slightly more complicated than that because normally the draw is done so that people don't play people from their own club and other constraints like that. Also it is not always possible to pair people with someone of exactly the same McMahon score (if, for example there are 3 people with a McMahon score of -10) so if someone might have a slightly harder game in one round, but then they should be given a slightly easier game in another round. It can even get more difficult than that if there are only a few people in a certain range of grades (for example suppose that there are people with McMahon scores of -15, -18 and -20, and no-one in-between) Then it may be necessary to have some handicap games.

All of the above doesn't really need to affect the players if they don't want it to. They can just turn up, do as they're told and have fun. And everyone gets a chance of winning something.

What else do you want to know?

The above description of the McMahon draw system came about because someone asked me about it by E-mail. Having spent some time answering their questions I decided to turn my response into this web page. If you have any other questions about the mysteries of a typical go tournament then feel free to ask. It can only make this page more informative in future.