Who Sits Out, and Why

When a club has more players than the courts can hold, some players sit out each round. This page explains how the app chooses them, why you may sometimes be unhappy with the choice, and why we could not make it perfect.

What we try to do

Two things matter, in this order.

1. Fairness. Nobody sits out a second time while someone else has not sat out at all, and nobody plays two or more rounds fewer than another player who is present. Everyone gets close to the same number of games.
2. Keeping the promise of a result. In Batman & Robin a win moves you up and, for a Robin, a loss moves you down. It feels wrong when you win and then do not get what the win earned, or lose and drop further than you should.

Why sitting out changes other people's results

A player who sits out keeps their place in the ranking, but does not take part in the next round. Everyone below them is grouped differently than if they had played. So who sits out decides how many players slide up or down a place, and a badly chosen bench can quietly undo somebody's promotion, or leave a winner sitting out straight after winning.

What the app does

The app picks the bench like this:

• Almost always: before every round it tries every sensible choice of who sits out, works out what each one would do to the results just played, and keeps the choice that disappoints the fewest players. Missed promotions count most; a winner sitting out counts less.
• The first round, and a tournament in which nobody joins or leaves and which is long enough for every player to have sat out once: the app keeps its original rule, which spreads the players who sit out evenly down the ranking. It does not look at results, so a winner can sometimes sit out. We found the original rule does better in that one situation, and the trying-every-choice approach does better in every other.

The Number of rounds setting in the lobby, default 6, tells the app how long the tournament will be, and so whether it can be that one situation. The organizer can change it at any time.

If you join late you are not compensated for the rounds you missed, so you simply play more of the remaining rounds.

Why it is hard

• Everything depends on everything. Moving one player off court changes the groups of everyone below them, so a good choice for one player can be a bad one for another.
• The results are not known yet. The bench is chosen before the next round is played, so the app has to choose without knowing who will win.
• Fairness gets in the way. By the end of a full cycle only a few players are still owed a turn on the bench, so the app has no real choice left. In that last round, someone who just won may have to sit out.
• Good ideas fail. We built and measured more than ten different ways of choosing, in simulated tournaments with identical results for each. Several that sounded right, such as simply benching whoever just lost, made things worse. The approach in use was the best of them that was fast enough to run during a live tournament; a slightly better one was too slow.

What to expect

In a typical short tournament, over many simulated tournaments, the app's choice almost never broke a promised promotion or demotion, and only rarely made a winner sit out. You may still, occasionally, feel disappointed: a winner can still sit out, especially in the last round of a cycle, and some sit-outs are simply forced by fairness. That is a limit of the problem, not something we overlooked.

You can sit out two rounds in a row, but only when a new cycle starts. In the middle of a cycle it cannot happen: a player who just sat out has played fewer games than everyone else, so they play next. Once every player has sat out once, everyone is equal again and the count starts over, so a player who sat out in the last round of one cycle can be chosen again in the first round of the next. The app allows this on purpose. Sitting out again breaks no promise, because that player has no result to keep, while putting them back on court can push someone else below the place their win or loss earned. A fixed order, such as always starting again from the first player, would not survive players leaving, joining, or courts being added.