Counting up goals and assists is a great way to evaluate players. 20 points in an 82-game season and a player is probably a fourth line talent; 50 and you’re talking second line territory; 60 and you’re getting into top-line material. However, there is much more to a player than just counting up the numbers. There are many advanced statistics that can give you a better picture of a player’s value to the team. The most common ones are Corsi, Fenwick, and Expected Goals (xG).
As the name suggests, these stats look at a hockey game and try to determine who is controlling possession of the puck. They do this by dividing the ice into small boxes and counting each shot that goes in during that box. The resulting values are called Corsi, or more specifically 5v5 Corsi Relative (CF% rel). They can also be broken down even further into blocked and unblocked shots to get a more precise number. These can be used to determine a player’s Fenwick (FSh% or FSh% if you want to include blocked shots) and expected goals as well to get a more complete understanding of a player’s contribution to the team’s total.
There are many different xG models available to the public, and they differ in how they account for various aspects of the game. However, most of them achieve the same thing: they predict the likelihood of a shot scoring given all the factors involved in the shot itself and the events that happened before it. The different models can sometimes yield slightly different results, but over the course of a year they’re generally quite close.
While examining these numbers on their own is important, it can be more interesting to see how they compare to each other. That’s where the slope charts come in handy. Slope charts plot a player’s individual ixG against their actual goals. A positive slope means the player is exceeding expectations, while a negative one indicates they’re underperforming.
These charts can be a fantastic way to find out which players are truly impressing their teams and which ones are just going through a rough patch. For example, the chart below shows how some teams have had their best scorers significantly outperform expectations this season, while others have been snake-bitten by underperforming players.
This visualisation is just one of many that can be made using the slope chart tool. There are many other ways that these charts can be useful, including highlighting the best team scorers in the league and identifying which players had the most luck or bad luck in terms of their expected goals this season. You can make your own slope chart by clicking the link below. It’s easy enough to create a chart for any team, player, or game in the NHL database. Just click the chart and enter the data you want to plot, then select “Slope” in the drop-down menu. You can also create a comparison graph by selecting “Compare” and choosing two different players or teams.