Last week we reviewed the advanced statistic “expected goals for”. It’s a metric that analysts will utilize quite a bit this season, so we thought it might be beneficial to provide a bit of an introduction to the stat for those not familiar. If you are still a little fuzzy about the stat, or need a refresher, here’s a quick recap.
Expected goals for is a statistic based on the aggregation of each exact shot attempt location and type of shot, and the historical success rates for those shots/types taken at each location.
For example, if Alex Ovechkin takes a shot from the top of the right circle, and historical data for that exact location says 5% of the shots have been goals, Ovechkin would be credited with a 0.05 expected goals for (xGF) value for that one shot attempt. The xGF values are summed over the course of a game or other time segment, yielding a resultant “expected goals for” (xGF) value. If Ovechkin made five shot attempts in a game with an aggregate expected goals for of 2.35, he earned an xGF of 2.35.
The same is calculated for the opposition while Ovechkin is on the ice. If an opposing player takes a shot that has a 3% historical value of scoring, while Ovechkin is on the ice, the opposing player is credited with the historical value of 0.03 xGF and Ovechkin is credited with an expected goal against (xGA) of 0.03.
We can sum the player’s expected goals for and expected goals against to achieve an overall expected goals differential, which would be 0.05 – 0.03 = +0.02. Anything in the positive conveys that the player is generating more scoring opportunities than the opposition when the player is on the ice.
2022-23 Preseason Values
Here is a look at the Capitals players and their expected goals differential (xGF – xGA) for the 2022-23 preseason, so far. [Click to enlarge].
There are no real surprises at the top of the list (the best differential). Lucas Johansen has the best differential among all prospects in camp that have played in a game. In other words, the Capitals are generating more shot attempts/better quality of scoring chances than the opposition when he is on the ice. Joe Snively and Hendrix Lapierre are a close second and third among prospects.
At the low end, Dylan McIlrath is really no surprise, as his brand of defense is a stay-at-home style. Connor McMichael has the lowest differential among all prospect forwards.
CAVEATS AND CONTEXT
As with ALL statistics, the expected goals differential metric is a single brush stroke to an overall painting. It provides part of the overall picture, but in no way should it be used alone to render an overall verdict or opinion on a player.
The current expected goals differentials presented above includes a number of significant variables. Players have played a different number of games, with varying linemates of varying expertise, against a wide range of opposing expertise.
By Jon Sorensen