About 4-5 years ago there were only a few people (including yours truly) who were publishing hockey data viz on a regular basis. Now, the number of hockey data viz publishers has seemed to double or triple in numbers. One of my favorites is Sean Tierney. He publishes a series of charts through Twitter on a regular basis and you can also go to his Tableau Public profile to view them on demand. They are simple scatter plots and trend line charts that are easy to understand, tell a great story, and best of all, he refreshes the underlying data 5-6 times a week.
I follow him on Twitter and sometimes re-tweet a particular chart if I think it is particularly illustrative of how the St. Louis Blues are playing. The scatter plots are always interesting to me because they show the relation between to given stats (usually a “for” stat and an “against” stat). You can see how those two stats relate to each other for the team and how the team relates to other teams in the league. However, the one question I always have when viewing these scatter plots is, “how has the team moved across the scatter plot during the course of the season?” Sean’s charts just tell us where the team is in terms of those stats as of the date he refreshes the data. What I want to know is, how has the team moved across these scatter plots during the course of the season.
My answer to this question is the “Season to Date” charts. These three charts show the how the relationship between for and against rates for shot attempts, goals, and then the save percentage and shooting percentage for the team evolves over the course of the season. These charts look sort of crazy so let me walk you through them real quick.
First, each line represents the “path” a team has taken during the course of the season in terms of the relationship between the two stats in the chart. The line starts at the beginning of the season which is marked with a one. The progression of the season can be followed using each point along the line and the direction of the line is shown by the shading. The first games of the season are dark blue while the more recent games of the season are bright red. Finally, the most recent game in the data set for the team is marked with the game number. In the case of the St. Louis Blues, they have played 52 games to date so the end of the line is marked with a 52.
Second, each point on the line represents a game and the team’s stats for the season through the end of that game. For instance, in the first game the Blues played this season, their corsi for/60 was 62 while their corsi against was 75. Skipping ahead to game ten the Blues’ corsi for/60 for the entire season through that game was 54 while their corsi against/60 for the season up through that game was 58.
These charts are designed not necessarily to view each point in isolation, but rather to view the pattern the line makes as it moves around the charts. For instance, when taking a look at the St. Louis Blues shot attempt rates, it took them about 15 games before they finally moved into the region where they were below the per game average for the league in corsi against/60 and above the per game average for the league in corsi for/60.
In terms of their goal rates, the team moved relatively quickly into below average for against/60 and above average for for/60. However, while the against/60 has remained relatively steady, the Blues goal scoring rate has been diminishing. The team save % and shooting % mirrors this trend as well. However, the team’s save % has been improving over the past few games (“Hello Starter Carter!”).
Here is the link to the charts in my Tableau Public profile. Please let me know if you have any questions about these charts and how to use them or interpret them. I want to give a special thank you to Alex Gable and Neil Greenberg for providing thoughtful and useful feedback about the design of these charts.