The game of hockey continues to morph and evolve at a frantic pace. Ten years ago, rolling out a D corps with three skaters under 6-feet would largely be an act of folly. And yet, here are the Bruins are — with Torey Krug, Matt Grzelcyk and Connor Clifton all playing a key role in Boston’s playoff run.
And now more than ever, coaching staffs are relying more and more on raw data and cold, hard analytics to help formulate decisions made to positively impact the product on the ice.
Count Cassidy among the new breed of bench boss.
"It does confirm things,” Cassidy said of incorporating analytics. “That's the first thing, the eye test. You're seeing what the data is telling you and I think coaches look at that a lot. We're stubborn a little bit, we like to trust our eyes, and I think that's what analytics is good for. It gives you an unbiased opinion. … I like looking at data and then using it accordingly. I don't get married to the — so many controlled entries, which is much higher than normal — but you do have to use certain points of it to reinforce the things you're teaching.”
For Cassidy, one area that both he and his coaching staff have focused plenty of energy on is in the O-zone, and the importance of quality over quantity when it comes to generating scoring chances.
While tracking Corsi Events (shots, blocks and misses) is a great way to approximate puck possession — and can be narrowed down to individual matchups or the overall production of a forward line or D pairing — Cassidy has stressed a defensive effort aimed at steering quality chances away from Grade-A areas in the slot, even if it means relinquishing some ice up at the blue line or opposing low-to-high sequences.
Keeping skaters out of the slot not only limits quality chances from in close against a goalie, but it also cuts down the risk for the high-danger chances that come from rebounds. It was something that Boston learned all too well against the Blue Jackets in the Eastern Conference Semifinals, with two of Columbus’ three tallies on the power play coming off of rebound strikes from Matt Duchene from an average of 9 feet out from Boston’s net.
"I do believe that teams that control the slot battle — and I think that’s eye test, too, but the numbers really back that up — win the majority of the games," Cassidy said. "I think, for me, you keep them out of the prime scoring area and you get to the prime scoring area, that's a big determinant, 5v5 obviously. … The rebound chances, that means you're getting inside.
“I guess that's the term, getting inside. We had trouble last year with Tampa. This year, we've been better. I thought we did a good job against Carolina, keeping them to the outside and whether you saw it the same way, when you were watching the game, I do believe it was one of the reasons why we didn't give up a ton of goals. Obviously, Tuukka (Rask) was another, specifically on their power play."
(During the Eastern Conference Final, the Hurricanes barely had much of anything to show for their scoring chances in the slot — with two of their four 5v5 goals scored from beyond the circles and around the blue line.)
So far this postseason, Boston has largely excelled at keeping high-danger scoring chances away from Rask — with the B’s netminder facing 3.4 rebound attempts per 60 minutes so far this postseason, with 10 other playoff goalies facing higher rates.
Meanwhile, down the other end of the ice, Carolina’s Curtis McElhinney faced 4.750 rebound attempts per 60 minutes (the fourth-most among goalies) — a sign of Boston’s increased effort to fire in high-quality looks from in close.
“Assistant coaches, I think it's real relevant,” Cassidy said. “Because they are a little more dialed into specifics. Like Jay (Pandolfo), how many rebound chances are we getting? He likes to do the O zone, so we went from, I think at the start of the year, we were 25th or 28th in the league (in rebound chances), I think we climbed all the way up to, I want to say — 12th, 10th? We moved up quite a bit. So he's pretty excited about that.”
In some regards, analytics have changed some of Cassidy’s approach when it comes to formulating a game plan — especially on the defensive side of things. During the regular season, there were 10 teams that carried the puck into the opposing zone in over 50% of all entries. Seven of those clubs were in the top 10 in goals per game during the regular season (Sharks, Flames, Capitals, Penguins, Blackhawks, Panthers, Avalanche). Naturally, the Bruins made an emphasis on forcing teams to dump the puck in and let their forecheck attempt to do the heavy lifting.
“Probably the neutral-zone defense,” Cassidy said of an area of the game that he has changed his thinking on thanks to analytics. “I was always, wanting to protect the blue line, but maybe not aggressively as we do now. Because the data has kind of showed us that more offensive opportunities, or better offensive opportunities, come from when you have control of the puck going over the blue line.
“Teams build their team around it. I think Toronto has been an example. They want to attack off the rush chances ... if you can defend the blue line and not let them in there clean, that's one I watch every day to make sure we're stubborn there.”
Of course, analytics are not the end all, be all for Cassidy — nor will he be putting together any PowerPoint presentations on expected goals or Corsi events in the Bruins locker room anytime soon.
But finding that balance between the “eye test” and the unbiased conclusions formulated by taking a look at the numbers behind a game has led to plenty of positives results for Cassidy and his crew.
“I don't think you can use every bit of data, you'll drive yourself crazy,” Cassidy said. “But I think it's relevant for certain things. I like the data, but I'm never going to go into the locker room Monday and say, We had 16 controlled entries last game against 20 ... I don't think the players give a crap about those raw numbers. That's more for us backing up what we're teaching and how we're executing.”
Stats via Natural Stat Trick, Evolving Hockey, and Sean Tierney.