The basic goaltending stats -- save percentage and goals-against average -- aren't the best measures when it comes to whether a goalie is performing well or underperforming.
Neither stat addresses a big factor, which is the type and quality of a shot goaltenders face. The play of the defensemen in front of a goaltender can have a big impact on their save percentage or goals-against average.
The statistic that aims to account for that is goals saved above expectation, or GSAx.
GSAx uses another metric, called expected goals, or xG
If you're unfamiliar with the concept of expected goals and why it is useful, here's a refresher from our advanced stats primer:
Expected goals aims to assign a value to a shot attempt based on several factors.
Factors taken into consideration include the type of shot (slap shot, wrist shot, etc.), whether the shot may have come off of a rebound or a rush, the location of the shooter (both distance and angle to the net), the talent of the shooter, and the state of the game (tie game, trailing, etc.), and more. Values of each factor are determined by the probability of each factor leading to a goal based on the data from past events.
The GSAx stat is simple. It's the expected goals against minus the actual goals against. If the result is a positive number, then the goaltender is outperforming expectations based on the quality of shots he faces. If the result is a negative number, the goaltender is allowing more goals than expected based on the quality of shots he is facing, meaning that he is underperforming.
It's still so early in the season to make any sweeping assessments of the seasons of Tristan Jarry or Casey DeSmith, who to this point have split time nearly evenly with Jarry making six starts and playing a total of 321:07 and DeSmith making four starts and playing a total of 294:25.
Neither have great basic goaltending stats. Jarry has a .859 save percentage and a 3.92 goals-against average. DeSmith has a .882 save percentage and a 2.85 goals-against average.
But are those numbers a result of facing more difficult shots due to the way the team is performing in front of them, or are Jarry and/or DeSmith underperforming?
This is where GSAx comes in handy, especially when you have a defense corps like that of the Penguins, which can greatly vary game-by-game based on who happens to be healthy in a given game. The GSAx stat evens the playing field and accounts for those changes in defense.
Using the data compiled by Evolving-Hockey, we see that Jarry's expected goals against (xGA) so far this season based on the quality of shots he's faced is 13.78. His GSAx is -6.85, meaning he's allowing more goals than would be expected based on the quality of shots he faces. His GSAx of -6.85 is the second-worst of all 64 goaltenders in the league this season.
The only goaltender with a worse result this season? Matt Murray, at -9.76.
Last season, Jarry's GSAx was .99, meaning that he performed better than expected over the course of the full season.
DeSmith has faced slightly easier shots, recording a xGA of 11.59. And like Jarry, he is also performing below expectation, although not quite as severely, with a GSAx of -2.47, good enough for 46th in the league.
The last time DeSmith was in the NHL, in 2018-19, he had a GSAx of .6, which means that he was also previously performing better than expected.
What does this all mean?
It's still so early in the season, but the numbers tell us that while DeSmith has fared better this season, both goaltenders are clearly underperforming. They're letting in soft goals.
While both have limited experience in the NHL to this point in their careers, we can see that in the cases of both goaltenders, they both performed slightly better than expected over the course of a full season. This is definitely a rocky start for the two of them, but we've seen in the past with each goaltender that through the highs and lows of a season, their highs can make up for the lows, and then some.
