By Leon Lifschutz | Follow me @BruinsBreakdown
The Bruins look like they will go into next season with a goaltending duo of Tuukka Rask and Jaroslav Halak. While Rask rumors swirled in the early days of the off-season, and after his abrupt bubble exit, he remains on the roster. Both player and the team have shared the expectation is for him to remain a Bruin. The two keepers boasted this past season’s least goals against and took home the Williams Jennings Trophy for their stinginess. Rask finished as runner up for the Vezina Trophy as top goaltender. The tandem has no doubt had success. With Rask and Halak well into their 30s, and the likelihood of a condensed game schedule, it will be important for the Bruins to maximize the performance of their netminders. Two key questions come to mind. First, does the data suggest the Bruins really need two high-level netminders? If so, what is the optimal number of starts for each goalie in order to get the most out of each one? Let’s do a little digging into the numbers, make some charts, and discuss.
The past few years have seen a shift in the mindset and subsequent deployment of the NHLs masked men. Long gone are the days of Martin Brodeur playing all the games and Mike Dunham merely serving as a target for practice. The NHL has begun to embrace the idea of ‘load management’, a concept much more prevalent in basketball, at least when it comes to it’s goalies. Perhaps this is for good reason. Kevin Woodley, of NHL.com and InGoalMag, points out the last time a goalie won the Stanley Cup after playing more than 60 regular-season games was more than a decade ago. With more back-to-backs in the NHL, the general belief is that you have a better chance to win if you start a different goalie in each game. While there is some debate over that, it has become common practice for NHL bench bosses including Bruce Cassidy.
The data seems to be aligning with the behavior of NHL GMs who have been demonstrating their desire to build tandems. Marc Bergevin and the Canadiens traded for Jake Allen and signed him to a nice contract to insulate Carey Price. The Dallas Stars re-signed playoff hero Anton Khudobin to a nice payday with some term to complement Ben Bishop. The importance of having two quality goalies was no more apparent during the recent bubble experience. Amongst the final four teams remaining, three did not hesitate to give starts to both netminders. Through our investigation, we will see if this trend should also matter for the big bad Bruins.
In order to determine how Coach Bruce Cassidy may want to dole out ice time to his goaltenders, we will take a look at their performance throughout their careers in relation to games played. We will examine four metrics – Save Percentage (SV%), Goals Saved Above Average (GSAA), Quality Start Percentage (QS%), and Real Bad Start Percentage (RBS%). All numbers are pulled from the invaluable folks at Hockey-Reference. These four numbers will allow us to assess Halak and Rasks’ performance. We can also insert trendlines which, while not perfect, will give us a visual displaying a peak that indicates the ideal number of games played. Before jumping in, it should be noted that while informative, our analysis is not necessarily perfect. For example, outliers exist like Halak’s terrible year in St. Louis where he only played 16 games. In 2014-15, Rask posted strong numbers, the year he set his career-high in games played. Goalies can sometimes be voodoo but that doesn’t mean we shouldn’t try and make some sense of them.
Rask-Halak Save Percentage by Games Played pic.twitter.com/8ZJHwmBXTV— BruinsBreakdown (@BruinsBreakdown) October 28, 2020
SV% simply measures the number of shots stopped versus those faced. SV% has quickly replaced Goals Against Average (GAA) in recent years as the standard-bearer for measuring goaltending performance. It is believed to be a truer measure of a goalies performance versus GAA which often is more a reflection of an overall team. Rask has been an above-average goaltender in this category his entire career and has had a number of years well above average. It is evident from his trendline though that too many games negatively impact his numbers. If we had to determine a maximum workload for Rask, we would likely want to do so around 50. Halak’s SV% peaks around the 40-45 game mark at which point we see diminishing returns.
Goals Saved Above Average
Rask-Halak GSAA by games played pic.twitter.com/Ihq6IxPfas— BruinsBreakdown (@BruinsBreakdown) October 26, 2020
GSAA utilizes expected goals models and subtracts actual goals scored to determine how a goalie measures up to what should be expected. The weight of each shot is determined by its location on the ice thereby creating a degree of difficulty measure for us to use when assessing goaltender performance. It is not a perfect stat as it does not account for pre-puck movement or traffic in front, both of which have a strong correlation to goals. However, the goalies our eye test suggest are better, generally grade out well on this metric meaning it can be a valuable stat within context. While Rask’s numbers are a little noisy, Halak’s are very clear. The Slovakian goalie posted all of his strongest seasons playing between roughly 30-50 games. Minimal playing time or too heavy a workload were not good looks for Halak. Rask, as noted, is a little more all over the map. However, according to his trendline the optimal number of games for him, at least in this category, is in the 40-50 range.
Rask-Halak Quality Starts Percentage by Games Played pic.twitter.com/99CWb12Pk2— BruinsBreakdown (@BruinsBreakdown) October 27, 2020
QS% is a stat developed by Rob Vollman in Hockey Abstract. If a goalie exceeds the league average SV% or stops at least .885% when facing less than 20 shots they receive credit for a quality start. Above 60% is considered very strong on the QS% metric. Rask has had some truly impressive years in this category. All of his most impressive years come in the 35-55 games played window. We can also note mostly lower scores as the games played get to the end of and exceed that window. Halak’s numbers are more consistent and bunched together though he doesn’t post any year quite as impressive as Rask. His strongest years seem to again fall into the 30-50 games played window.
Real Bad Starts
Rask-Halak Real Bad Start Percentage by Games Played pic.twitter.com/Vmtgp7d0WL— BruinsBreakdown (@BruinsBreakdown) October 28, 2020
RBS% is also a metric developed by Vollman. These are games where a goalie has posted an SV% lower than .850%. Note that this chart is inverted so we could utilize trendlines in the same direction as the others. In this situation the lower the number the better. Halak continues the trend of consistency living in the 10-12% range across most seasons. His trendline would suggest that 35 games are the ideal number before we see a slight decline. Rask’s trendline is very clear. As he exceeds 50 games his propensity for bad starts increases.
It is evident that both goalies do their best work when sharing the load. The Bruins were wise to adopt a tandem approach and it seems necessary for their continued success. This was especially true as Rask rounded 30-years-old. After three seasons between 2014-15 and 2016-17 in which the dynamic Finn played his most – 70, 64, and 65 games played respectively – Boston finally dialed back his workload. As a result, the Finnish netminder has twice finished top-ten in Vezina voting after not having placed in votes since 2013-14. Though Rasks’ numbers are less consistent, the trendlines across a number of metrics suggest his ideal number of starts is roughly 45-50. Halak is the absolute ideal 1B on your depth chart. While he doesn’t bring gaudy underlying numbers, he consistently performs well enough to give the team a chance to win. A heavy workload has not proven in his best interest and his ideal number of starts, accounting for Rasks’ needs, is around 35, a perfect fit for his role with the Black and Gold. For the upcoming season, the Bruins have a great tandem and have seemingly found the formula to maximize their success.
While the Bs are set in the short term, both goaltenders’ contracts are set to expire in 2021. The Bruins front office will need to decide what direction to go between the pipes at that point. All signs point to needing a strong pair to share the load whether it’s made up of the current incumbents, includes a prospect like Jeremy Swayman, or another free agency find like Halak.