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Flames Adjusted Zone Shift - UPDATED


JLikens of the always interesting Objective NHL blog has been working on a few things this off-season, one of which is adjusted zone shift. We've discussed this metric in the comments now and then, but here's a full explanation for those unfamiliar:

One thing I wanted to look at was changes in zone, the guys who are getting the puck going in the right direction. And since the NHL doesn't publish their zone time information any more, I just went by faceoffs. If a shift started in the defensive zone the the player gets a plus, and a minus for starting in the other end of the rink. Also if your shift ends in the offensive zone you get a plus, and you get a minus if your shift ends at the bad end of the ice.

Star-divide

This is the method for determining a players raw zone shift. JLikens looked at the stat and decided an adjustment was in order:

It appears that starting a high proportion of your EV faceoffs in your own zone relative to your team average - in other words, having a high PLAYER ZONE DIFFERENTIAL - is pretty favorable toward ZONE SHIFT.

...

Long story short: It's easier to have a good Zone Shift number if you're starting more in your own end of the rink relative to your teammates, and if the metric is to be worth anything at all, this ought to be corrected for.

And I've attempted to do exactly that. Contained below is a listing of the league's best and worst players in ADJUSTED ZONE SHIFT - adjusted because the stat attempts to control for the above bias.

Meaning the results were being skewed towards defensive forwards and defensemen. He has a full explanation of his adjustment methodology at the linked article, but, in short, J subtracted the players starting and ending zone ratios from the teams starting and ending ratios. There's probably more to be done on this issue, but this is a good first step in my estimation as the top and bottom players in the league by adjusted ZS seem to pass the initial sniff test.

Anyways, J was good enough to send me the adjusted ZS numbers for the entire Flames club, as follows:

The results are fairly surprising. Aucoin, Moss, Glencross, Langkow and Giordano come out looking pretty good, while guys like Boyd, Bourque, Iginla and Phaneuf apparently struggled. Boyd is to be somewhat expected, but that so many good players were so far in the red makes me scratch my head. The entire club seemed good at moving the puck forward last year, but one wonders if the Glencross/Moss/Conroy line was driving the bus in this regard even more than was suggested previously. 

JLikens will no doubt be adding to this body of work as the summer matures, so expect a follow-up in the near future.

UPDATE -

JL recently sent me this reponse to the issues raised in the comments:

The numbers are different for two reasons.

1.  The numbers at Vic's site don't include shifts that ended in goals at EV, and my original numbers didn't take that into account.  However, the data that I've sent you includes shifts that ended in goals.
 
2. The correction formula is slightly different now due to changes made to the data (namely, the correction described in 1).
 
Also, it should be emphasized that each player's adjusted zone shift (and this applies to unadjusted zone shift, too) is a team relative stat.  Accordingly, it's somewhat biased against players on strong teams (zoneshift, wise).  The Flames players with poor (adjusted) zone shift numbers have only done poorly relative to their teammates.  I suspect that most of Calgary's players are pretty effective at moving the puck in the right direction in absolute terms.

Hopefully this clears things up a tad. 

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Kent, there seems to be something not quite right here. Giordano’s adjusted number here shows as 15.14. On J’s page, he shows an adjusted number of 19.2. Further, the second highest player in his top 100 is Rich Peverley, with an adjusted number of 34.22. On the Flames-specific stuff he sent you, the adjusted numbers for Moss, Glencross and Aucoin are all higher than 37. Am I misreading something? I’m just using the numbers off the main page of his website, since I can’t seem to open the Google Doc.

by Robert Cleave on Jul 22, 2009 10:13 AM PDT reply actions  

You’re right, Rob that’s pretty screwy. Perhaps “expected” is the adjusted in this spreadsheet, but even then the signs aren’t same as the spreadsheet he shares at his place. I’ll fire off an email today for an explanation.

by Kent Wilson on Jul 22, 2009 11:30 AM PDT up reply actions  

The overall results are not that surprising to me because I think the Flames had a terrible defensive season last year, although, I do agree that it seemed that they were moving the puck well in the right direction. I haven’t, however, seen many stats that indicate this is true.

I was surprised to see Aucoin’s number so high. I thought he wasn’t as bad as I expected, but I didn’t think he was great.

Overall though, I go back to Regher’s comment about Keenan’s style being flawed, or missing. Iggy went from +27 to -2 (w/ -23 zone shift), Lanks +16 to +1 (9.8zs) Phaneuf +12 to -11 (with -33zs) and Regher +11 to +10 (11.6zs). We also have more than covered Kipper’s down turn from .909 to .903 sv%.

That’s a collective drop in our top four from 07/08 – 08/09 of -68! and approximately 8-10 additional goals by Kipper. Somehow the stats all seem to point at full systems disaster for our big money earners and a huge load carrying by the likes of GlenX, Conroy, Moss and offensively by Bourque. This only seems to reinforce that point. Good find.

by LawrenceS on Jul 22, 2009 10:13 AM PDT reply actions  

The Flames were one of the best outshooting teams in the league last year in terms of corsi. They also take way more offensive draws than defensive draws. The puck was cetainly moving in the right direction most of the time, especially at ES.

I’m going look into these numbers…

by Kent Wilson on Jul 22, 2009 11:32 AM PDT up reply actions  

yeah, you’re totally right – I see the Flames were 2nd in the league in Corsi at +717, but also 14th in the league at +/-. That’s from Kulas Korner anyway. My sloppy writing, I still use +/- as an indicator for defense and am only new to corsi for offense. I guess I was meaning that offensively the Flames looked decent, but haven’t seen much to show they were not terrible (from the top 16 playoff teams) defensively, which seems to jive with this latest post and the big drop in elite Flames’ +/- numbers.

Is this how you prefer to look at Corsi and +/- (offense and defense) because I always find the discrepancy quite interesting? Calgary being 2nd corsi, 14th +/-. Whereas Boston was 13th/1st and Pittsburgh 21st/7th

by LawrenceS on Jul 22, 2009 1:34 PM PDT reply actions  

Corsi is truer measure of a team’s strength in that it’s not susceptible to “luck” (ie; percentages) which is notoriously fickle and tend to revert to the mean over the long term. For example, I noticed back in November that the Blue Jackets were routinely outshooting their opponents, but were losing due to some crummy goaltending and bad SH% of their best players. I predicted then they would be in line for a turn-around. Similarly, I noticed in February that the Panthers were well under water in terms of outshooting, but were in a play-off spot simply because Vokoun/Anderson were playing out of their minds. That’s when I wrote the post that said it would be a mistake to not trade Bouwmeester.

Think of corsi as “possession” or, even better, a measure of how much time a team spends in a given zone. If a club is deep under water, it means they spend more time trying to stop goals that trying to score them and vice versa.

by Kent Wilson on Jul 22, 2009 2:23 PM PDT up reply actions  

Shorter Kent Wilson: Kipper can’t fuck up a team’s Corsi number ; )

by Robert Cleave on Jul 22, 2009 2:27 PM PDT up reply actions  

Sure, but there’s got to be more we can take from it than that because I don’t think Lundkvist was screwing up NYR’s numbers (6th corsi +405, and 23rd +/- at – 20) as well I don’t think Biron was so good that he saved the Flyers (24th corsi 347, and 6th +/ at +24) Especially considering these two goalie’s performances where so similar when isolating SV% and GAA, with Lundkvist being slightly better. Is there the equivalent of a defensive Corsi or do we just have +/- ?

by LawrenceS on Jul 23, 2009 10:55 AM PDT up reply actions  

I don’t know why that is crossed out

by LawrenceS on Jul 23, 2009 10:56 AM PDT up reply actions  

Don’t think of corsi as either defensive or offensive exclusively. It’s a total “strength of a team” thing. It’s a “how much time do we spend in each zone” thing. The Flames last year tended to spend more time in the offensive zone than the defensive zone at ES because they had 3 relatively solid lines up front (4 when Roy wasn’t dressed). However, they were still relatively mediocre defensively since they tended to give up high quality shots during the time they found themselves in the bad end of the rink.

by Kent Wilson on Jul 23, 2009 11:35 AM PDT up reply actions  

The Numbers

Ya gotta account for the high dump-ins over Jarome and Robyn’s helmets. They would never shy away from chasing the biscuit for a give-and-go, or an icing call. Now, that’s a Nice Effort, the nascent rise of a great Stat for sure, but be reasonable about it, as well. Congrats. What is it again? Adjusted Zone Shift. Cool.

by Niulrana on Jul 22, 2009 4:43 PM PDT reply actions  

The numbers as they sit are inaccurate. Im waiting for a correction from the author as we speak. Nothing should be taken from the table as it sits.

by Kent Wilson on Jul 22, 2009 5:02 PM PDT reply actions  

What if you’re shift doesn’t start and end in a faceoff? Would that shift even be included in the population?

I don’t think you’re doing a good job of “measuring the direction of the puck” if you’re only capturing a small percentage of total events. This is a really crude metric.

by mclea on Jul 22, 2009 10:16 PM PDT reply actions  

That’s a fair point. Lots of shifts end as a dump in or a neutral zone face-off (off-sides). Still, there are also lots of events that end in either the offensive and defensive zones – Bouwmeester saw some 500+ defensive zone face-offs and 300+ offensive zone draws last year alone, for instance. I can’t say for certain what percentage each eventuality represents.

I don’t think I’d give zone shift much weight alone. Still, it adds a layer of context.

Also, I’m glad to see you re-surface mclea.

by Kent Wilson on Jul 23, 2009 9:39 AM PDT up reply actions  

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