One of the reasons I really enjoy digging into the field of hockey analytics is that big breakthroughs are still being made.
Unlike in baseball, where everything that can be measured has probably already been measured, hockey still has so many unexplored nooks and crannies — or at least undefined.
One of the more exciting concepts that is being pursued currently by professionals and hobbyists alike is the concept of shot quality. We inherently know shot quality exists, but quantifying it has been a slow process until recently. However, thanks to great work by Emmanuel Perry of Corsica Hockey and several others, hockey has an Expected Goals (xG) model to swish around its collective mouth.
The basic concept behind the xG concept is that it uses probability and past precedent to estimate how many goals a team should have scored and allowed, giving us a better idea of pure performance.
Deconstructing a Season
Obviously, the real goals are the only ones that count, but if you’re into predicting what’s going to happen, xG has proven to be the most predictive of future goal differential than any other team-wide metric at our disposal.
With that knowledge in hand, we can further explore how teams like, say, the 2017-18 Penguins have performed throughout a given season.
Cole Anderson at Crowd Scout Sports has further broken down xG into the following component parts: Even-strength play, goaltending, special teams and shooting percentage.
As such, I found the following Anderson tweet about the Penguins’ down-then-up season quite fascinating:
the Wild have a similar profile to YTD PIT Penguins, with slightly better goaltending results. PIT had been on a shooting hot streak until last night pic.twitter.com/YJRq2WNN8j
— Cole Anderson (@CrowdScoutSprts) March 11, 2018
As you can see from the chart, the only consistently positive part of the Penguins’ game this season has been special teams. While the penalty kill has gone through a bit of a down spell recently, the power play’s top-ranked conversion rate has provided a reliable lift game-in and game-out, which has been reflected in the steady green xG line you see above.
On the other side of the consistency coin, the Penguins’ shooting success has gone from awful to excellent over the past couple of months. Sanity has been restored on a team featuring two-time Richard Trophy winner Sidney Crosby, soon-to-be three-time 40-goal man Evgeni Malkin and the sniper known as Phil Kessel.
As I talked about last week on my Big Picture podcast, the Penguins still lag behind their highly-skilled peers when it comes to finishing their shots as a group, but as Anderson’s xG model suggests, they are now ahead of the pack in finishing if you factor in the quality of chances they’re generating.
Good News, Bad News
I’ve been writing about this for a couple of months, but the Penguins have done better in the second half of the season in generating more shot quality for themselves and limiting that quality to opponents. The blue line on Anderson’s chart indicates that progression, which has been quite steady throughout the year. That’s the kind of improved process Mike Sullivan wants to see.
Regardless of the reason for it — the Antti Niemi experiment, Matt Murray‘s family crisis, unproven rookies as backups — the Penguins’ goaltending started on a bad foot and really hasn’t been able to dig out of that hole since.
This isn’t exactly a surprise, as the Penguins’ five-on-five save percentage of .908 ranks dead last in the NHL, but looking at these numbers indicates the team defense isn’t as much to blame as it is the men wearing the masks.
According to Anderson’s xG model, goaltending has cost the Penguins approximately 20 goals over the first 69 games.
That’s sobering for sure, but there are X-factors at work here, too.
For one, Murray had the goaltending on the uptick prior to his concussion. Once he comes back, we’re talking about a 23-year-old who still holds a slightly-above-average .918 save percentage for his career and who’s performed very well (.928) under the playoff spotlight.
Still, for all the angst over line combinations, trades, focus and motivation, the clearest conclusion from the xG sample is that the goalies simply haven’t held up their end of the bargain in the three-peat quest. Yet.