One area hockey analytics have had real trouble quantifying over the years is defensive play. You can look at how a team suppresses shots when a player is on the ice, but coaches and general managers always want more information that is a bit more clear-cut. Considering how much of a defenceman’s job is to take care of their own zone, it’s an area where we can certainly expand our knowledge.

One of the most important elements of defence is a player’s ability to acquire the puck in the defensive zone, and move it out of danger. The most advantageous way of doing this is with a controlled zone exit, whether by passing the puck to a teammate outside the defensive zone, or skating it out. However, despite its inefficiency, dumping the puck out has value as well, if you successfully clear the zone.

It would be tempting to look at players simply with a high volume of these plays, but defence is more complicated than that. If a player is stuck in their own zone often, odds are that they’ll still have a high number of defensive zone exits, the puck will just come right back in. So the first filter we would need to apply to the raw zone exit numbers would be what percentage of a defenceman’s successful plays with or for the puck are in the defensive zone. What we find is that an average defenceman makes 61.7 per cent of their plays in their own zone, a huge number.

Knowing how many plays a specific defenceman makes in their own zone per 20 minutes played at even strength, we can then calculate what percentage of those plays result in controlled zone exits, or total zone clearances.

Again though, playing defence is not so simple. If a player is extremely aggressive, or high event, they may rack up many successful zone clearances, but also turn the puck over in the defensive zone at a very high rate, so we have to consider the percentage of plays a player makes that results in a turnover as well.

If we want to find an excellent transition defenceman, we also have to look at how often they get to loose pucks. Some players may be proficient in exiting the zone but struggle to win battles, relying on a strong partner beside them. If you’re looking at the best of the best, you want a complete player, so we’ll include loose puck recoveries, but not just in raw form, also as a percentage of a player’s total defensive involvement.

So we’re looking at players who play a lot, are very involved in the play, have high raw zone exit numbers, but also see zone exits and loose puck recoveries represent a large percentage of their plays with the puck. Couple that turnover rates, and we can see who is most efficient.

I wanted to keep it to the top 10, so there are some very excellent defencemen who didn’t make the cut. Because we’re experimenting, I took the top eight players in controlled exits, and top eight players in total zone exits, and there was a significant amount of overlap, coming up with our top 10 zone clearers.

There are some expected names in there, along with a couple of surprises. Mattias Ekholm has long been a player that analytically inclined writers have been hailing, and he shows well here, with a similar breakdown to P.K. Subban, although with fewer loose puck recoveries and a higher turnover rate, meaning he likely leans a bit more on his defensive partner than Subban does.

Subban for his part, is an odd one. He clears the zone a lot, but he also leads the group in dump outs, something that is new to his game this season. In fact, Subban dumped the puck out of the defensive zone half as often last season, which may show that he has taken the “safe play” rhetoric of his coaching staff to heart. Subban’s defensive game has taken a hit overall this season due to that change, though the rate at which he recovers loose pucks still leads the pack, which helps mitigate some of the damage.

The big surprises on the list are probably Dmitry Orlov and Ryan Murphy, who have gone under the radar this season despite excellent campaigns. Murphy in particular just does not dump the puck out, and while he could stand to be more involved in the play overall, you have to admire that in a young player. Orlov could also be more involved in the play, as with Murphy they are two of the three lowest event defencemen in the group, but again, excellent numbers for a young player.

Mike Green is another surprise, as no one has talked about him much since he signed with the Red Wings. Green has sparkling zone exit numbers, doesn’t spend much time in the defensive zone relative to his peers, and has a low turnover rate. He could win more battles for the puck, and he may have had a disappointing first season offensively with Detroit, but his play in his own end has been a bright spot.

Cam Fowler is a very interesting case, as he is very high event, very efficient exiting the zone both with and without control, and has one of the lowest defensive turnover rates in the NHL, but he is far below team average in shot suppression on the Ducks. Of the top 20 players in this style of breakdown, Fowler does spend the most amount of his effort in the defensive zone, with 65 per cent of his events happening there, but I wonder if he’s more in a bad situation than just poor defensively.

The least involved defenceman of the entire group is Nick Leddy, but he is also easily the most efficient at clearing the zone overall, though he doesn’t win many loose pucks. This suggests that while Leddy is fantastic with the puck on his stick, he does need someone else to get it to him more often than other players.

The reigning Norris Trophy winner, and likely first back-to-back winner since Nicklas Lidstrom in 2008, is ripped constantly for being a defensive liability, but that doesn’t hold water here. Erik Karlsson is the second-highest event player in the NHL behind Victor Hedman, spends the second-least amount of time in his defensive zone of the players in this group, has a below-league average turnover rate in the defensive zone, and exits the defensive zone like it’s nothing. Combine this with his offensive ability? Just give him Norris number three now.

Saving the most interesting for last, young Morgan Rielly of the Toronto Maple Leafs has been very impressive this season. Of all the players in this breakdown, Rielly has the highest percentage of his defensive zone events accounting for recovering the puck, and exiting the zone. Rielly acquires and distributes the puck on 74.2 per cent of the plays he makes out of the defensive zone. His turnover rate is higher than the best of the best, but at just 22-years-old, he is incredibly impressive.

None of this paints a complete picture of defensive play, but it is a start to expanding our understanding of the kinds of plays that produce good defence, and perhaps what coaches are looking for when evaluating players with the so-called eye test.