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Why we should be wary of what Cassidy’s hire means for Bruins

The Bruins removed the interim tag from coach Bruce Cassidy, but was his end-of-season success really a sign of what's to come?

It wouldn’t necessarily be accurate to say the Bruins were in a tailspin when Claude Julien was fired. Boston had lost two-straight, including a 6-5 barnburner against the Toronto Maple Leafs, in the days leading up to Julien’s firing. But the reason Julien was let go wasn’t the losses alone. It was a combination of things. 

With the consecutive defeats, the Bruins had fallen out of a post-season spot. Despite the high-scoring affair with Toronto, Boston was struggling to produce offense with any consistency. Defensively, there were also some struggles, and the Bruins were in the bottom half of the league when it came to goals against. Now consider Julien had been spared previously when it appeared his job had been on the line and that the Bruins were in danger of missing the post-season for a third-straight year. Take all of it into account, and maybe it wasn’t all that surprising Julien was shown the door.

By the same token, though, few were blown away when Bruce Cassidy came along that the Bruins turned things around. At the time of Julien’s firing, Boston was among the most underperforming clubs in the league, if we’re talking strictly in terms of wins and losses. The Bruins were a dominant team who simply couldn’t find a way to score and at times couldn’t buy a save. Their combined shooting and save percentage at 5-on-5 — also known as PDO — was 96.7. No team in the league was performing worse, not even the last place Colorado Avalanche, and given the Bruins’ team talent the situation was bound to correct itself.

Things sure did start looking up under Cassidy, too. Over the final 28 games, Boston went 18-8-1, a record that put them among the league’s 10-best teams across the final two months of the season. As the wins came, so, too, did the reignited playoff hopes, and while the worry about missing the post-season didn’t exactly dissipate, Cassidy’s Bruins clinched a playoff berth in the final days of the campaign and booked a date with the Ottawa Senators in the first round. And despite the six-game exit at the hands of those same Senators, Cassidy’s apparent turnaround of the Bruins in just two short months is a big reason why he was named the head coach Wednesday, seeing the interim tag that had been placed on his promotion from assistant coach removed. 

We should be wary of what the result of the hiring may actually be, though.

First, credit where credit is due. The Bruins under Cassidy had a better winning and points percentage than they had through the first 55 games under Julien. This much we know. And it’s worth admiring the areas Cassidy did improve Boston during his brief stint with the club this season. 

The biggest was on the power play, where the Bruins became one of the most lethal teams in the league with the man advantage, boasting a 27.8 percent success rate under Cassidy. Only two teams, the Edmonton Oilers and Buffalo Sabres, managed better marks from Feb. 7 onward. Cassidy’s Bruins were also a better chance generating team at 5-on-5 than Julien’s Bruins were. However, there was only a marginal increase between the two squads. Under Cassidy, Boston generated 7.74 chances for per 60 minutes, whereas they managed 7.02 with Julien at the helm.But the truth is the impact Cassidy had on the team may have been largely superficial. Despite the increase on the power play, which was helpful, and the increase in scoring attempts, there wasn’t a single notable category in which the Bruins’ improvement was apparent. 

Let’s start with the base statistics for those who have no time for the advanced stats argument. Cassidy’s impact on the power play was impressive, but the penalty kill didn’t fare as well under the Bruins’ new coach. While the dip was only slight, Boston went from second-best in the league when down a man to the seventh-best penalty killing squad. As noted, though, the dip was only a mere 1.1 percent. The difference in shots on goal under Julien and Cassidy was the biggest difference, though.

While it’s only slightly apparent on the penalty kill, where Cassidy’s Bruins surrendered about half a shot more per 60 minutes, it’s all the more obvious how much better Boston was at controlling the play under Julien when looking at 5-on-5 numbers. In terms of pure shots on goal, the Bruins surrendered almost .60 of a shot fewer per 60 minutes under Julien than they did under Cassidy. At the same time, Julien’s Bruins also produced nearly five more shots for. Boston’s shot for percentage dipped more than four percent under Cassidy. That’s quite the swing.

And that’s where we start getting into the statistical debate, because some will posit that it doesn’t matter much if the Bruins were generating more or less shots under Cassidy because those attempts came from better areas to score while attacking and areas that were more easily defended and stopped in the defensive zone. Boston’s slight improvement in scoring chances for per 60 at 5-on-5 is a hint that there may be a bit of truth to Cassidy’s system putting his top flight players in better scoring areas, but defensively, the Bruins were nowhere near as sound. In fact, Julien’s Bruins allowed a mere 6.25 chances against per 60, whereas Cassidy’s squad saw 7.38 against. The result was a scoring chance for percentage of 52.9 percent with Julien at the helm and 51.2 percent once Cassidy took over.

It’s not just scoring chances, though. It’s the entire process that leads up to it. Without getting into too much of a numbers slog, here are the categories where the Bruins were better before Cassidy took over: Corsi for and against, Fenwick for and against, shots for and against and, finally, expected goals for and against. All eight categories, and the Bruins’ respective percentages in each category, dipped from Feb. 7 onward.

Of course, those who want to talk only about results and not consider process will point purely to goals for and goals against rates. It’s indisputable that both improved under Cassidy and, yes, his Bruins won a greater percentage of their games because of that. But remember that little PDO thing we talked about? It’s no coincidence the Bruins were at 100.9 at 5-on-5 under Cassidy, which is good for the eighth-best mark in the league from the time he took over. Only nine of the league’s teams were that good throughout the entire year, so reaching the mark again is no given.

The truth is Julien had to go at some point and that Cassidy came in and got the Bruins into the post-season is no small feat. He did a sound job coaching this team into the playoffs. And none of this is to suggest Cassidy is a bad coach or the out-and-out wrong choice for the job, because, in fairness, we’ve yet to see what he can do over the course of a full season with this club. 

However, given everything we understand about underlying numbers and their impact on success, it’s hard not to have questions about Cassidy’s full-time hire. If Boston’s underlying numbers take another step back in Cassidy’s first full year, we might not be seeing the 18-8-1 team that ended this campaign but a Bruins team that’s scratching and clawing to get back into the post-season once again.

(All advanced statistics via Corsica)

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