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Who has been Driving the Bruins Offense?

Using early passing data to gain insight into the Bruins offense

NHL: Detroit Red Wings at Boston Bruins Paul Rutherford-USA TODAY Sports

The data presented in this article is just 5v5. We will explore the powerplay at another time. 5 games is also an incredibly small sample. This is more for entertainment than a true analysis.

Looking at the Bruins offense as a team

At 5v5 this season, the Bruins have 13 goals in 246.5 minutes. That rate is good for 9th in the league. But goals, in small sample sizes, can be misleading. When looking at the Bruins shot rate, they are 12th in the league with 49.60 shot attempts for per 60 minutes. This isn’t bad, especially considering the Bruins are a defense-first team, even under Bruce Cassidy. However, the concern is with the Bruins shot quality.

As the chart above shows, the Bruins shoot above (red) the league average rate on the perimeter, but are below (blue) league average at shooting from the slot. This is reflected in their expected shooting percentage, which takes into account length of the shot, angle of the shot, whether or not the shot is a rebound, and more. The Bruins have an adjusted (teams tend to have a higher shooting percentage when leading) expected unblocked shooting percentage of 5.11%. That is good for 30th in the league.

Natural Stat Trick keeps record of scoring chances using shot location. 10 of the Bruins 13 goals came from scoring chances. This is not surprising as most teams fall somewhere in this range. The Bruins are 29th in scoring chances per 60 minutes at 5v5, but 12th in goals from scoring chances per 60 minutes. This is because of their 18.5% shooting percentage on scoring chances, which is 6th in the league.

I also keep track of scoring chances, but I have a tighter area than Natural Stat Trick. I use the more traditional, home plate area and count all shot attempts whereas Natural Stat Trick only counts unblocked shot attempts.

From my data, the Bruins have 60 scoring chances in their first 5 games this season. Of those 60 scoring chances, 29 were unassisted (48.3%), meaning there was no pass completed prior to the shot, nor was the shot a deflection or rebound opportunity.

Shots with dangerous pre-shot movement are deflections, rebound opportunities, shots after cross-ice pass in the home plate area, and shots from a pass from behind the net. The Bruins have had dangerous pre-shot movement on 17 of their 31 assisted scoring chances (54.8%).

Of the other 159 shot attempts that were not scoring chances, only 64 were unassisted (40.3%). But only 13 of the 95 assisted shots had high-danger movement (13.7%). So the Bruins are taking advantage of their scoring chances partly due to a high proportion of dangerous pre-shot movement.

Introduction to Passing Data

In 2014, Ryan Stimson decided to track the New Jersey Devils player’s passes leading to shot attempts. Since then, he and others have performed valuable research on the game of hockey. This data has provided a better way of predicting player’s future points, gives us better context of for the data we have (corsi-for percentage, expected goals, etc), and even bridge the divide between coaching tactics and analytics. I will be tracking these stats for the Bruins throughout the season, and hopefully writing about the results bi-weekly or monthly. Here are a few basic stats that will be used.

Shot Assist - In most cases, this is a pass leading to a shot attempt. However, shots that are tipped, or shots that create a rebound are also shot assists.

Primary Shot Contribution (PSC) - The sum of a player’s shot attempts and primary (last before the shot) shot assists.

Primary Shot Contribution Percentage (PSC% or PSC_per) - It is the percentage of Bruins shots while a player is on the ice that he either took or assisted on. (PSC / CF)

Primary Shot Contribution Index (PSC_I) - Primary Shot Contributions per 60 multiplied by Primary Shot Contribution Percentag.

Assist to Shot Ratio - Shot Assists divided by individual shot attempts.

Don’t worry if you didn’t soak all of that in. I will explain the stats and their usefulness when I use them.

Having data on passes leading up to shot attempts can give us insight into playing styles, line and player chemistry, and who is driving offense for the Bruins. Luckily, the biggest story line surrounding the Bruins right now is lines. Ryan Donato sat a game along with Danton Heinen the next game. In place of them was Joakim Nordstrom on the second line. Line juggling is something we expect to see in the future. Can we use some of our passing data to evaluate players’ performances so far? Of course we can.

The chart above is each player’s primary shot contributions per 60 minutes of play so far this season. We see a runaway train in David Pastrnak, a second tier of Jake DeBrusk and Patrice Bergeron, and a group of players with many contributions like David Krejci, Brad Marchand, and John Moore who leads defensemen in this metric.

Outside of points, the only place we can traditionally, directly credit a player with offense are his individual shot attempts. When we add shot assists, we see a much better picture of who is directly creating offense for the team. For players like David Pastrnak and Jake DeBrusk, this is not an issue. They lead the Bruins in shot attempts per 60. But what about a playmaker like David Krejci?

The playmaking abilities of David Krejci are far beyond that of his fellow teammates. He leads the team in primary shot assists with 14.5 per 60 minutes of play at 5v5. So although David Krejci is 17th out of the Bruins 19 skaters in individual shots per 60 with 6.0, his 20.4 (rounding) primary shot contributions per 60 are 5th on the team. He has certainly been a radical player in this regard, but Brad Marchand being second in assist to shot ratio and primary shot assists per 60 is also something to look out for.

But some players might be on the ice for less shot attempts per hour than their peers, and that is where primary shot contribution percentage and primary shot contribution index come into play.

We’ll start off with primary shot contribution percentage. As you see here, Jake DeBrusk leads the way. He has a shot attempt or a primary shot assist on half of the Bruins shots he is on the ice for. In my opinion, this metric is better to be used across lines. The Bruins top line has run primarily through Bergeron and Pastrnak while Marchand lags behind. The successful fourth line has been carried by Sean Kuraly.

The weakness of primary shot contribution percentage is that it punishes players who are on the ice for a lot of shots. For example, the Bergeron line is so good at producing shots that it is hard to directly contribute to a large portion of the shots. In order to try to find a middle ground, we can index it.

This seems to be the most fair look at how Bruins have been contributing to the team’s offense. DeBrusk and Pastrnak are far above the others. Bergeron and Krejci are neck and neck for 3rd and 4th on the team. As you would expect if you’ve been watching the Bruins, Heinen and Donato lag far behind, but we have a pleasant surprise in Anders Bjork and his playmaking abilities.

After five games, there is not much to make out of this just yet, but this may give us a few things to watch for moving forward.

  • Could Sean Kuraly return to 3C? Bruce Cassidy said before that he is not ruling that option out. There is a lot more to it, but if Sean Kuraly continues to prove that he can contribute offensively better than David Backes, Cassidy may want to promote him in hopes of three scoring lines.
  • Will the trend of Bjork over Donato and Heinen continue? This isn’t something we really expected going into the season, especially with Donato’s offensive talent. The gap will surely close, but will the two overcome Bjork, or is he the best of the three in this regard?
  • I didn’t mention this yet, but if you haven’t noticed, McAvoy is primary shot contributions per 60, primary shot contribution percentage, and of course, the index. I don’t expect this to continue at all. You can’t predict regression, but I wouldn’t be surprised if he hit a hot streak in the next couple of weeks.