On Sunday, the NHL’s website published my long read on the place of analytics in hockey and why they are so critical. As you know if you read it, it contained a lot of material, and good for you if you managed to understand it all. It was the product of months of revising and editing, and in the end a complete section needed to be cut. I made the decision to cut that section – which focussed on evaluating defense – in order to add substance to the other sections, and because I didn’t think it entirely fit. Here is that section:

EVALUATING DEFENSE WITH ANALYTICS

Evaluating defense is an area in which analytical findings have helped to shape perception. Conventional analysis dictates that the best players at preventing goals do so through proper positioning, good stick-work, blocking shots and hitting the opposition. Those things can be important when the other team has the puck, of course, but they don’t paint a full picture of a player’s effectiveness at preventing goals.

Phoenix Coyotes Coach Dave Tippett once discussed a particular issue he was having in analyzing his defensemen, while he was coaching in juniors.

“We had a player that was supposed to be a great, shut-down defenseman. He was supposedly the be-all, end-all of defensemen. But when you did a 10-game analysis of him, you found out he was defending all the time because he can’t move the puck.

 Then, we had another guy who supposedly couldn’t defend a lick. Well, he was defending only 20 percent of the time because he’s making good plays out of our end. He may not be the strongest defender, but he’s only doing it 20 percent of the time. So the equation works out better the other way. I ended up trading the other defenseman.”

Tippett was ahead of his time in thinking about defending in a completely different way. A player that has the puck is contributing both on offense and defense at the same time. So a player can be below average without the puck in his own end, but still wind up better at preventing goals than a traditional defensive defenseman.

“Defense is the sum of actions that reduce the number of shot attempts your team surrenders over the course of a game,” explained Stephen Burtch of Sportsnet.ca.

“This can take numerous forms (breakouts, cycling, pinching) that involve a player’s team being in possession, and that may or may not translate to offense. But they definitely translate to fewer chances for the opposition which arguably makes them defensive skills and not offensive.”

The ability to keep the puck out of the defensive zone becomes especially critical when considering the role of randomness. When a player spends time in his own end, he opens up the possibility of a seeing-eye shot, or a deflection, or a fluky bounce, or just a perfect placement, resulting in a goal against. No matter how good that player — or even an entire team — might be at defending, over large samples the opposition will find holes, take advantage of lapses, and inevitably win games. Watching a player block shots and seal off passing lanes may mislead a viewer to presume that said player is having a positive effect. But playing in the defensive zone means putting yourself at the mercy of randomness. The saying that “the best players make their own luck” is true because the best players spend as little time as possible in their defensive zone, limiting shots against and thus the potential for pucks to find their way into the net.

Basing defensive evaluations mostly on defensive zone play is a flawed practice, as has been demonstrated through an analysis of years of data. Traditions die hard, however, and beliefs that conflicts with what parents, coaches, and television personalities have taught us about the sport for decades are generally dismissed.