Statistical Analysis

Tracking Stats: Zone Defence and Keeping the Other Team Out

Last time I wrote about tracking zone transitions, we discussed Zone Exits by defencemen. Now, in part two, we discuss Zone Defence.

I’ve noticed that, of all the things I track, people seem most interested in Zone Exits. Of course, exiting the zone is important. Some times it seems to overshadow an equally important skill set: keeping the opposition out of the defensive zone in the first place.

 

Zone Defence

Just as there’s Controlled Zone Exits, there’s Controlled Zone Entries. Many have written about the benefits of entering the zone with control of the puck as opposed to dumping it in, but I go back to Jen Lute Costella and her wonderful primer on zone entries. For the 5 of you who are reading this but haven’t read her yet… do so!

The take home is this: Teams that allow the opposition to carry the puck into their zone give up more shots than teams that force the opposition to dump it in… and it’s not close. This makes sense. If the other team carries the puck in, they maintain possession, they’re more likely to get a shot off, and get more scoring chances. If they dump it in, the first thing they have to do is get the puck back. It’s much less likely to lead to a shot.

So your goal, as a defender, should be to:

  1. Deny the opposition from entering the zone at all (Zone Entry Denial)
  2. If “1” isn’t possible, force them to dump it in so that they have to try to get it back (Uncontrolled Entry)

Last year I tracked Zone Defence for 30 Oiler games. I found that Oiler defencemen who allowed fewer controlled zone entries also had fewer shot attempts against. Further, in games where the Oilers defence core allowed fewer controlled zone entries, the team did better in shot attempt metrics.

It does seem that being aggressive at the blue line and preventing the opposition from entering the zone with control is a skillset that helps the flow of play. McLellan appears to be emphasizing this as part of his defensive structure. Darnell Nurse described in an interview back in October how they’ve “worked on killing (attack) plays before they start, pinching off pucks right before the blue (line) or just inside it.”

 

What I’ve Been Doing

I’ve been tracking how Oiler defencemen do at preventing the opposition from gaining the blue line. This next section is long and perhaps dull. However, I want to be open and clear about my definitions, allowing me to refer back to this post in any future one.

Targeted

First, for every zone entry by the opposition, I determine who was the primary defender on the play. I only track when an Oiler defenceman was specifically targeted on a zone entry. Some rules determine who was targeted. Usually it’s just the player that was closest, and most able to defend, the opposing player who got the puck across the blue line. If it’s a 50/50 call between two players, I defer to the defenceman as being targeted. If both players are defencemen, the defenceman responsible for that side of the ice is targeted.

Untargeted

I still track zone entries where an Oiler defenceman wasn’t targeted. I label them as “untargeted” and code them to the defenceman responsible for that side of the ice. So, if a forward is the primary defender on a zone entry, that’s coded as “untargeted”. Another example is a dump in from the red line where the opposing player made no attempt to gain the zone and was under no pressure (say they wanted to go for a line change or were dumping it in straight from a neutral zone face-off). Most untargeted entries are when the other team dumps it out from the offensive zone and the puck slides into the Oiler zone without leading to an icing.

Odd man rushes are also “untargeted” unless a defenceman’s actions directly led to the odd-man rush. For example, if Klefbom gives the puck away in the neutral zone leading directly and immediately to an odd man rush, he gets credited as being ‘targeted’ on that zone entry. Likewise, if Sekera makes a bad pinch with no forward back to cover for him and that leads directly to a 2-on-1 on Russell, Sekera is ‘targeted’.

Overall, in games I’ve tracked this year, 62% of all zone entries against the Oilers were ‘targeted’ on a defenceman. The vast majority of the untargeted entries (83.6%) are uncontrolled dump-ins. I’ve included them in my tracking as a check. I can always analyze my data by including these untargeted entries in the future in case there’s concern that there’s bias in how I determine someone to be ‘targeted’.

Denied vs Controlled vs Uncontrolled

Once I know a defenceman’s targeted, I code whether a zone entry was “denied”, or whether the entry was “controlled” or “uncontrolled”.

A denied entry requires that the opposing team have possession of the puck in the neutral zone and the defender causes them to either lose possession of the puck or regroup. Intercepted passes are coded here as long as there is a clear target on the opposing team that would likely have gotten possession if the defender didn’t step up. Forcing the other team off-side due to a play at the blue line or a forcing an icing due to a play before the red line is also a denied zone entry. Dump outs by the other team from the offensive zone where the Oiler defenceman recovers in the neutral zone are not coded as denied entries.

A controlled zone entry is literally just the opposition getting into the zone while maintaining possession of the puck. This is usually skating it in, but sometimes is via a pass. In the case of a pass, I code the controlled entry against the defender guarding the pass recipient. The opposing team has to retain possession of the puck for at least one second in the Oilers zone for them to get a controlled entry. So, if Darnell Nurse cuts a winger off just inside the blue line, forcing a dump-in, that’s still an uncontrolled entry.

Uncontrolled entries are what’s left. Usually these are dump-ins, but could also be a player losing control of the puck due to a solid hit or a poke-check.

 

So How Did the Oilers Do?

I’ve tracked 37 of the first 41 Oiler games this year, missing games 14, 28, 29, and 36. I may go back and do those at some point to complete the data set. However, with Corey Sznajder doing the whole league this year, my tracking is essentially obsolete the second he completes his dataset. So I’m also viewing my work as an interim while we wait for his whole project to be complete.

 

The data here is fascinating to me for a couple reasons. Firstly, if we ignore all the players with small sample sizes (less than 10 games), there is a narrow window in the “% controlled entries allowed”. Everyone is within about 5%… except for Russell. We’ll get back to him in a moment.

This narrow gap is not what I expected. Last year when I did this project in a sample of 30 games, there was a much wider range between players. Among players with at least 10 games tracked, there was 23% between best (Sekera) and the worst (Oesterle) and a much wider range in between. The zone denials had a 13-percentage point gap between worst to best, which is now at 9% due to Russell and 5% without him.

New Additions?

Some of that can be explained by better personnel. Sekera and Klefbom were at the top of the chart last year with similar numbers (39% and 40% respectively). They are now joined by newcomer Adam Larsson who is essentially equal to Klefbom and Sekera. All three of them are clearly playing unsheltered top 4 minutes. Meanwhile, Benning has been revelation in a bottom-pairing role. I knew he had some puck skills and that he had logged big minutes playing top competition in the NCAA with the weakest defensive partners. I did not expect him to play such a significant role, albeit in sheltered minutes. He leads the team in preventing controlled entries.

However, new additions don’t explain all the improvement. I tracked almost the same number of games of Darnell Nurse last year and while his zone denials are the same, his controlled zone entries have improved by 14 percentage points! Gryba is in the exact same boat, with similar numbers to Nurse last year and a similar improvement.

How do we make sense of this? How did Nurse and Gryba magically improve at the same time while two major additions to the Oilers roster (one defensive specialist and one raw rookie) also show well by this metric?

Coaching?

My suspicion here is that McLellan has coached his entire defensive unit to be more aggressive at the blue line. We saw it in Nurse’s comment quoted earlier. It’s seems too coincidental for a defense core that was so widespread in this particular skill last year to suddenly be so narrowly collected. I think we’re seeing team effects here. I also wonder if we’re seeing the benefit of having three good defencemen in the top 4. This allows guys like Nurse and rookie Benning to play on a sheltered 3rd pair where they are better able to succeed (though I don’t believe that alone can explain Nurse’s improvement).

There were also so many injuries last season, that I imagine it was hard for McLellan to implement his defensive strategy in his first year. Klefbom, who is great at this metric, was injured in December. Davidson was gone for the last third of the year. Schultz, who was mid-range, was traded. Ference and Nikitin started the season getting some games in before being pushed out. Oesterle and Reinhart were regulars in the top 4 by the end of the season. Clendening was a waiver claim who played through middle-late part of the year only to be replaced by later waiver claim Pardy. Fayne was in and out of the NHL.

That’s a lot of turnover in a coach’s first season with a new team.

So this year, with a number of repeat customers, a second training camp and more familiarity with the team, we’re seeing the defensive group as a whole show more aggression at the blue line.

 

Rising Tide Doesn’t Float All Boats

Not everyone is enjoying increased success, though.

I wouldn’t read too much into Fayne’s number as he’s only played 3 games. It’s worth noting that his denial percentage is similar to last year and his controlled zone entry percentage is within 5%, so this may not be far off his ability, despite the small sample size.

Davidson is the real surprise here. He was 3rd on the team in 14 games tracked last year at 42% controlled entries against. He really hasn’t been himself coming back from injury. Although I’ve seen improvements in other parts of his game as he plays more, this one aspect is still lagging. I remain optimistic that we’ll see a return of the Davidson of last year.

 

So… Russell?

Which brings us to one Kris Russell. He certainly stands out, doesn’t he? He, alone, of the top 4 (in fact, of everyone with at least 10 games) struggles to defend the blue line.

It’s interesting, Russell doesn’t actually get beat at the blue line often. He just leaves a large gap and cedes the zone, instead engaging within the defensive zone. It’s quite striking especially when he plays with Sekera, who is among the more aggressive of the D. Despite both of them being left-handed shots with single digit numbers, I can usually tell them apart simply by how aggressively each of them is playing their man coming in to the zone.

The result is that Russell doesn’t look bad playing defence. He rarely gets beat after all. He’s pretty good at engaging once within the defensive zone. He blocks shots and breaks up plays. The issue is that even if you’re really good at those things, if you keep letting the puck into your zone over and over again, it will eventually burn you. You’re ceding territory and you’re not going to be able to block every shot or break up every play. Even when you do those things, the other team still has the puck in the zone and can always pull up and set up position.

I postulate this as one reason why Russell seems pretty good by eye to many and gets credit for a lot of defensive plays, yet looks poor in shot attempt numbers. It’s curious that Russell plays this way almost uniquely among the Oiler regulars. You would think, if it’s a tactic thing, that it would be coachable. If my theory about McLellan is right, why doesn’t it apply to Russell?

 

A Theory

It’s worth pointing out that Russell is the sole defender tracked here that has regularly been playing his off-side. We know that playing two defenders of the same handedness on the same pairing leads to, on average, a startling reduction in corsi equivalent to 6 shot attempts per 60 compared to opposite handed partners. I don’t know how playing on your off-side impacts your zone entries against numbers. However, I did note that last year, the worst defender with at least 10 games tracked in this skillset was Oesterle, who played primarily on his off-side.

Of course, two examples don’t mean much and I’m not drawing any conclusions here, just raising questions. It’s also worth noting that Russell largely played on his left side last year in Calgary and his shot attempt numbers were quite poor there. I was not tracking his zone entries against, but I believe his gap control was poor based on observations made by others. So, I’m not suggesting that is the secret to the Russell Problem.

However, it is fascinating to me that there’s a significant gap in Russell’s performance on the left and right side. Russell has played 7 games largely on his left side. I’ve happened to track 6 of them. In those six games, his controlled entry percentage was 41%. That is right on par with the rest of the defensive regulars! His controlled entry percentage in games where he plays largely the right side… 56.6%

Again, I’m not concluding from this that Russell’s poor controlled zone entry percentage is entirely due to him playing the off-side. I’m just posing the question. I think the most likely explanation here is that Russell is poor at gap control, that he’s been playing this way for years and it’s hard to undo a habit, and the better numbers on the left side is simply due to random variance captured by a small sample size. Still… it’s a trend I hope to follow if Russell gets more games on the left side.

 

Summary

I intended to explore so much more in this post. There’s looking at denials and controlled entries via frequency of those events. There’s comparing targeted to untargeted zone entries to see if there’s a significant difference. Another interesting piece is that Klefbom gets targeted on zone entries against significantly less often than any other regular defenceman. I tracked how defencemen do in puck retrievals off dump-ins when they’re under pressure. Alas, this post is already almost 3000 words. You all are probably tired of reading if you made it this far. Those further explorations will have to wait for another day.

Suffice to say for now that I’ve been tracking the majority of Oiler games and the zone defence numbers for the group as a whole have improved since last year, based on my tracked sample. Some of this can be explained with better defencemen. I suspect some is due to the team as a whole being more aggressive at the blue line, which may have been driven by McLellan.

Davidson is still rounding in to form and has a history of doing better. Russell, though, is lagging behind in this particular skillset. It’s possible that playing on his off-side impacting this. However, I have only limited evidence to suggest that is the case so far. It’s not like he was an analytics darling playing on his proper side last year. It’s just curious that other defenders have improved under McLellan and new arrivals have stepped up, but Russell continues to play a neutral zone game that is significantly different than the other defenders on his team.

 

What’s Next?

Well, there’s all those things I mentioned in the first paragraph of the summary. I’ve also been tracking all defensive zone passes, including whether the pass is sent to the defensive partner, the forward or is a turnover. The result is some interesting data about what happens in-zone when the Oilers’ defencemen have the puck. Perhaps I’ll share that next.

Now I just need to find time to write between all this tracking! (And, you know, my actual life!)

 

Raw Data?

You’ll note I didn’t include all my raw data in this post. The problem is that there’s a lot of it and it’s all in a format that isn’t easily posted in a blog. However, I’m more than willing to share my entire data-set if you’d like it. That includes full totals and game-by-game numbers for each defenceman. Just message me on Twitter (@wheatnoil) or email me (wheatnoil@gmail.com) and I’m happy to share.

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