First Reason for Losing: Poor Save%
What are some the reasons the Oilers were losing before Nelson and during Dallas Eakins time? The main problem was horrible goaltending. And before the reader blames the poor goals against on defense, this season's defensive stats--Corsi-Against and scoring chances against--do not show that the Oilers were allowing more shot attempts or scoring chances than previous seasons. In fact, under Eakins, the Oilers were better in these metrics. Thus, the terrible goals against can be squarely blamed on the goaltenders.
Has the Oilers' goal tending improved since Nelson? Scrivens' adjusted save% (5v5) before Nelson was 90.9% and Fasth's was 90.2%. After Nelson (excluding the shared coaching time with MacTavish), Scrivens is 91.7% and Fasth is 91.2%. With an improvement of 0.9%, this translates into 5 fewer goals against over 23 games (547 shots against) . In 1-goal games, which the Oilers have had many, that's the difference between a loss and a tie, or a win. The reason, then, for improvement in goals against is most simply explained as regression to the mean. Most goalies regress toward a 92% save% (except for the few elite goaltenders like Lundqvist). In other words, due to variance or "back luck," the goalies were under-performing under Eakins, but under Nelson they are playing closer to their "true" ability. Is it logical to attribute an improved save% to Nelson's coaching? I prefer the simpler explanation: regression to the mean.
Second Reason for Losing: Poor Shooting%
The other problem the Oilers were having under Eakins was scoring. Have they generated more even-strength (5v5) shot attempts and scoring chances with Nelson compared to Eakins? With Eakins, the Oilers 5v5 Corsi differential was 50% and the scoring chance differential was 49.4%. Under Nelson, the 5v5 Corsi differential is 46.6% & scoring chance differential is 41.8%. Thus, at 5v5, the Oilers offense generation has worsened under Nelson. No doubt the permanent loss of Perron, in addition to the injury-loss games of Hall and Pouilot have contributed to this drop in offense.
But what about shooting%? The Oilers shooting% has been poor, but this is a tricky metric.It doesn't necessarily reflect team ability to score. It tends to regress toward 8% regardless of team. For that reason, it's considered a "luck" or "variance" variable much like save%. Before Nelson, shooting% was 6.7%. After Nelson, it's 7.6%. This translates into 5 more goals over 23 games. Again, similar to improved save%, this is a case of regression to the mean.
Now one could say the Oilers shooting% has improved because they are crashing the net more, deflecting more shots, and screening the goalie more. If this is true, we would see an increase in scoring chances. But as we saw above, scoring chance differential has declined under Nelson, not improved.
It's All About Regression to the Mean
To summarize, the Oilers goaltending has regressed toward the mean as has their shooting%. Both these statistical factors have boosted the goal differential by 10 goals (5 for & 5 against) compared to these metrics during Eakins' period. These statistics happen on their own as more games are played, specifically, short-term unusually high or low numbers in shooting and save percentage gradually level out to their respective averages over the long-term.
All that being said, one sets of factors has improved under Nelson and that is special teams. Before Eakins was fired, the Oilers' special teams ranked 14th to 18th, which dipped even further under MacTavish and Nelson. (The power-play is reliably measured with Corsi-For per 60 min & the penalty-kill is reliably measured with Corsi-Against per 60 min.) Based on my possession-based ranking system, under Nelson, their PP moved up to 7th and the PK improved to 12th. When separating Eakins' from Nelson's period, the differences are even more pronounced. As noted by Jonathan Willis, under Nelson's time only, the Oilers' PP ranks 4th and the PK ranks 3rd. I will credit Nelson for improving the special teams.
Win/loss records and goal differentials can be deceiving over short periods of time. They are not reliable indicators of what's actually happening due to the randomness in goals in smaller samples. Thus, what we're seeing as improvement under Nelson at even-strength is somewhat illusory. What's occurring is regression to the mean. Nonetheless, I will acknowledge Nelson has made improvements to the team--based on measurable evidence--with respect to special teams, which is good. But the drop in even-strength performance is a concern and shows that the team really isn't all that better overall.
I'll also acknowledge, though, that losing Perron (traded to Pittsburgh) and losing Hall to injury (the Oilers' best possession and offensive player) is contributing to the team's weakened Corsi and scoring chance metrics. Thus, I am not implying Nelson is making the team worse. The loss of top-6 forwards like Perron, Pouliot, and Hall has undoubtedly figured strongly into the Oilers reduced offensive generation.
Thanks for reading! I welcome your feedback and criticism. If you don't agree, let me know (with your reasons, of course).
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Notes. Data courtesy of war-on-ice.com.
Addendum: I didn't realize Jonathan Willis had provided a similar analysis about 5 days ago. We pretty much come to the same conclusions. One thing Willis did was break down who was scoring more to improve the team's shooting%. According to Willis, the improvement can be completely attributed to Eberle's scoring. Over the last 5 games, I think you can also add Yakupov's scoring, whose goal-scoring is long overdue. Thanks to Derek Roy's self-appointed mentoring, Yakupov's scoring is finally "regressing to the mean."