If I decided to define a stay at home defenceman, the descriptors would generally start with terms like size, toughness and grit—a player who blocks a lot of shots and clears the crease and sacrifices his body for the team.

As fans we are easily seduced by these types of players, because they are defenders of the crest we have emotionally thrown ourselves behind. When our team has been slighted or disrespected, these behemoths rise up and throw bodychecks, fight and block shots and literally bleed for the team. They defend our honour. Unfortunately this seduction blinds us to reality. Rarely would descriptors like zero offensive skill, a struggle to clear the zone and make transition passes, or poor skating be attributed to this breed.

These specialists are forced to continuously defend because they struggle to move the play forward. These players understand their own limitations. They realize the penalty for turning the puck over by doing something outside their skillset far outweighs the risk of firing it off the glass, waiting for it to return to the zone so they can be praised for throwing bodychecks and blocking shots.

It isn’t simple rhetoric. Dave Tippet learned this lesson and used data to buck conventional hockey wisdom while he was a GM in the IHL.

“I’ll give you an example,” he told AZ Central. “We had a player that was supposed to be a great, shut-down defenceman. 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 defenceman.”

Unfortunately Dave Tippet is not the norm in the NHL and GMs can still be fooled by the shutdown defender. The Montreal Canadiens have been seduced by Douglas Murray, and they traded a superior player because of toughness and other meaningless stuff.

After the Canadiens dealt Raphael Diaz on Monday, the discussion centered around him being too soft. He was a non-scoring offensive defenceman who became expendable with the emergence of Nathan Beaulieu. The problem is that the Canadiens dealt a superior player to give ice time to an inferior one who at best can be described as physical and slow.

The shutdown perception allowed Murray to supplant Diaz even though he is the inferior defensive player. Every metric that exists says he is inferior. One look at extraskater.com exposes this fact.

The player usage chart tracks where players start the play, as well as the difficulty of their opposition. The players with the highest amount of defensive zone faceoffs and toughest matchups are located on the upper left. The players with the easiest zone and opponent matchups are located on the bottom right. Red bubbles equal poor possession. Blue equals good.

We can see that Michel Therrien shelters Murray against the top competition and starts the majority of his ice time in the offensive zone. Even with this disadvantage, Diaz is still on the ice for a higher percentage of goals and shots for. Even though he is placed in a more difficult situation to succeed, he still pushed the play forward better than Murray.

Diaz’s defensive numbers were helped by his offensive skills and ability to transition from his own zone. He spends less time defending, but even when he does he limits the damage at a better rate then the “pure defensive specialist”. I used the shot quality data to isolate Murray vs. Diaz this season at even strength. I tracked all the shots in their defensive zone and mapped them.

We can see above that Murray allows more high quality opportunities than Diaz. He gives up more slot opportunities, forces his goaltender to stop pucks in transition and allows almost double the deflections. The only advantage he has is that his crease-clearing ability is worth three less shots against. So his toughness, on average through 199 shots, saved .14 rebound goals more than Diaz but exposed Carey Price and Peter Budaj to two more goals on transition and deflection attempts.

One issue with this data was their combined performance, so I removed all common shots when they were on the ice together. That exposed Murray as an even greater defensive liability.

Murray’s numbers dropped in every category when separated from the more defensively responsible Diaz. But Diaz remained the same player. Murray over Diaz is what happens when you misidentify the factors that lead to defensive success. Size and toughness without skill is not better than skill without size and toughness.

In a vacuum, signing a player like Murray isn’t a franchise crippling move. When it becomes a concern is when players like Murray and Parros begin to force out superior players like Diaz.

Murray remains a lightning rod in Montreal not because of the type of player he is, but because of what he represents. He is the poster boy for a management team that has decided that possession, which has a proven correlation to winning, is less important than toughness and grit, which have a much weaker correlation.

As the data gets better, we slowly inch toward a paradigm shift in hockey. Eventually, we will define a defenceman who lacks the passing and skating skills to begin transition as a poor defenceman, not a stay-at-home defenceman. Until then though, players like Murray will continue to get a regular shift and players like Diaz will be labeled soft and defensive liabilities.