Curlometrics

Sabermetrics has come to curling.

A Bob Weeks column in today's Globe and Mail describes a curling sabermetrics project (and book) by Dallas Bittle and Gerry Geurts. The pair operate the curlingzone.com website, on which the article is reprinted here.

For those who know even less about curling than I do, here's a quick summary. This is from memory. There's probably lots of stuff wrong in it, because I don't watch curling much.

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Curling is like shuffleboard on ice. Teams take turns sliding rocks towards a bulls-eye area at the other end of the rink, eight rocks for each team. (The area with the bull's eye is called the "house," and the bull's eye itself is the "button.") After all sixteen rocks are thrown, the team with the rock closest to the button gets a point. It gets an additional point for each additional rock that's closer than any of the opponent's rocks. So if the rocks closest to the button are, in order, red, red, red, and yellow, the red team gets three points. Sometimes there are no rocks left in scoring territory, in which case both teams score zero.

I think it's called "curling" because if the rock is spun when slid, it will hook to one side instead of sliding in a straight line. This allows curlers to curl one rock in behind another that would otherwise be in the way. When the rock is sliding, the other team's players can sweep the ice in front of the sliding stone. This causes the rock to curl less, and also to go faster. The player who threw the stone (or the team's "skip," which is the player/manager/captain guy) will watch the stone's progress and scream at the sweepers to tell them when to sweep more vigourously ("hard, hard, haaaaaaaaaard!").

Each sixteen-rock sequence is called an "end," which I think of as like an inning in baseball. A game is ten ends.

The team that scored points in the previous end has to go first in the next end. This is a disadvantage, as the team with the last rock usually can find a way to score. The advantage of last rock is called "the hammer." When the team without the hammer is the one that scores, it's called a "steal."

There are four players on each team; each throws two consecutive stones. The positions are named "first", "second", "third", and "skip." The skip is the best player on the team – he or she goes last, and therefore gets all the glory. The guy that goes first doesn't seem to me to have a very interesting job, but I'm sure real curlers would disagree.

In Canada, the biggest men's tournament of the year is called the "Briar," or, officially, the "Tim Hortons Briar." Women have the "Scott Tournament of Hearts." (Tim Hortons makes the best coffee on earth. Scott is the toilet paper company. "Hearts" are little red shapes stereotypically associated with women – I don't know why men don't get their own stereotype, like the "Tim Horton's tournament of Tonka Toys" or some such.)

Here's the Wikipedia entry on Curling.
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From the article:

"Bittle's newest measure is something he calls the power triad, a combination of three statistics. There's hammer efficiency [how often a team scores more than one when they have the hammer], steal efficiency (how often it steals a point...), and scoring differential.

"They also devised new ways to score individuals ... that ... present a more detailed look at a player's skills."

I couldn't find anything about those statistics on the website, but that might be because a curlstat.com, which is linked to, is down. But there's a link to the book ($18.95 Canadian).

Also on the website is an heading "Curling with Math." It's got one article in it, calculating the best strategy for a given situation in the ninth end. One interesting thing is that it gives some win probabilities for the tenth end:

Odds of winning if tied with hammer (x) = 75.7%
Odds of winning if one down with hammer (y) = 39.5%
Odds of winning if two down with hammer (z) = 11.7%

These aren't probabilities for the end itself, because I think they include the chances of tying the game in the 10th and winning in extra ends.

The fact that the article casually throws win probabilities around suggests that the field of curling sabermetrics is reasonably well-advanced. I'm looking forward to reading more about it.