Corsi, shot quality, and the Toronto Maple Leafs

v00d00daddy

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Oct 9, 2007
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I'm not very clear on how all the advanced stats work and what they represent but I'm curious as to why shot quality is not considered a legit thing.

Is it because it's difficult to qualify or what?

How is a shot from centre or from the corner equal to a point blank shot from the slot?

Surely people recognize that not all shots are created equal.
 

Semantics

PUBLIC ENEMY #1
Jan 3, 2007
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At some point the world is going to have to acknowledge that corsi, fenwick, pdo, etc are just not very good for trying to predict the future. Especially in a game like hockey.

They are actually *extremely* good for trying to predict the future. That's why they've become so popular in the first place -- they have a better track record at predicting the future than the official standings. The Leafs may just be an outlier, an exception to their usual predictive power.
 

billybudd

Registered User
Feb 1, 2012
22,049
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I'm not very clear on how all the advanced stats work and what they represent but I'm curious as to why shot quality is not considered a legit thing.

Is it because it's difficult to qualify or what?

How is a shot from centre or from the corner equal to a point blank shot from the slot?

Surely people recognize that not all shots are created equal.

Two reasons

1) the stats community has come up with predictive models not involving shot quality

2) too many variables go into "what's a quality shot" to easily represent numerically

So instead of trying to get to the bottom of how to represent "shot quality," the tendency is to say "over a long enough timeline all teams will give up the same percentage of quality shots," even though a scatterplot/heatmap or, Hell, a pair of eyes can show that this is unambiguously wrong.

It's like those ancient representations of the solar system that had planetary orbits that reversed themselves. It worked most of the time, so the people who believed in them fought against anything challenging the orthodoxy of the model, even though the model was obviously illogical.
 

Master_Of_Districts

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Apr 9, 2007
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Personally i love that the Leafs are giving a big ol' middle finger to advanced stats. Tonight's game was a perfect example of that, we were outshot 38-14, but the Leafs absolutely had much better scoring chances. Of the 38 Wild shots, probably less than 10 of them were closer than 15 feet away from the net. I am 100% ok with giving up the amount of shots that we do because the majority of them are nothing shots from the perimeter. That's the system Carlyle plays--own the middle of the ice, collapse around the goaltender and keep the shoooters high and outside. It works damn well and the moment the other team makes a mistake in our zone we jump on it and produce a high percentage scoring chance off the rush.

I was expecting Uncle Randy to come in and try and force an offensive team to play defense first hockey, but in his time here all he's done is basically add structure and zone strategy to Wilson's offensive system. The Leafs are the most dangerous team in the league off of the rush, and we can expect to see a lot more games where we score more than 3 goals off 20 or less shots. We now have the personnel to disrupt the opposition's forecheck and cycle, which leads to odd man rushes. Im totally ok with being outshot 38-14 because on any given night now we have the quality goaltending to pull it off. Don't expect the Leafs to "regress to the mean" any time soon. Their game is now based around the aforementioned strategy.

http://www.nhl.com/scores/htmlreports/20132014/PL020082.HTM

Shots closer than 15 ft:

MIN - 4
TOR - 2

[Recorded shots taken from that close are pretty rare.]

Shots 15 feet or further:

MIN - 33
TOR - 12
 
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Cassano

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Aug 31, 2013
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The Leafs are playing a very unsustainable brand of hockey. It is actually very mindboggling that they've accumulated these many wins over the past season and thus far.
 

Hammer Time

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May 3, 2011
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http://blog.philbirnbaum.com/2013/10/corsi-shot-quality-and-toronto-maple.html

Interesting theory on why the Leafs had such a successful season last year despite poor corsi/fenwick close numbers.

Interesting article. Shot quality effects tend to be underestimated quite often in the stats community.

However, I do take issue with Birnbaum using raw Corsi (it looks like he's using raw Corsi because 44.1% was the Leafs' raw 5-on-5 Corsi last season) and comparing it with shooting percentage. High shooting percentages lead to more goals, which means the team is more frequently in the lead and score effects will come into play, lowering their Corsi. His conclusion is that Corsi is "too biased by situation and shot quality to be taken on its own". But this is something most analysts already know - and that's why stats like Score-Adjusted Fenwick, Corsi/Fenwick Tied, etc. exist - to limit score effects.

Would you rather have 3 quality shots on goal or 20 from the outside with no traffic? the answer is obvious. Any stat that goes by total shots is just flawed to me, at least some of the time which means the stat can't be totally trusted.

This isn't baseball where eventually everything evens out, there are variables in hockey that make these stats fun and everything but they don't tell you everything. Corsi shows us the top teams and the worst teams, so do the standings.

Against most teams, 3 quality shots. Against Toskala or Dubnyk, I'll take 20 easy shots. :laugh:

But like the old cliché goes, good things happen when you throw the puck on net. If you could choose between 3 quality shots or 3 quality shots plus 17 easy shots, which one would you pick? Gaining control of the puck and putting it on goal is generally a good thing, even if it's not everything. Even Carlyle recognizes this - in his post-game interview last night he said "we're going to get our butts kicked most nights if we play like this".

It's not the Leafs winning 6 games. It was like this all last season too. Going back to Carlyle's time with the Ducks they were similar as well. The difference is that under Martin the Habs were one of the best defensive teams in the league. No such accolades for the Leafs. They are nowhere near the level of defense that Martin's Habs were. Also under Therrien the Habs didn't play off the rush like the Leafs do, they peppered the goalie with shots til they scored. In fact there really is no comparison to made lol.

The year that Carlyle's Ducks won the Cup, we don't have Corsi or Fenwick stats available, but they did outshoot their opponents heavily. The other time they had a good playoff run (2009), they had a 50.1% Fenwick Close and 50.9% score-adjusted Fenwick. The one time the Ducks made the playoffs with a low Fenwick (2011), they needed a brilliant performance from Hiller, and were knocked out by Nashville in the first round with Hiller sidelined with vertigo. So generally, even with Carlyle the pattern is that good things happen when you outshoot your opponents in the long run.

Here's some food for thought for people fixated on shots on goal.

In 2009-10, the Leafs ranked 3rd in the NHL for CORSI (+422). We averaged 34.6 shots per GP. Only 4 teams had more shots and they finished 3rd, 7th, 1st and 8th respectively in league standings.

Anyone want to hazard a guess where Toronto finished in league standings? 29th overall.

Seems we've been defying CORSI for a lot longer than people think. Well that or there are certain things that are far more relevant to the outcome.

Corsi and Fenwick measure the effectiveness of a team's skaters at even strength. It does not cover goaltending or special teams (and Corsi doesn't even consider shot blocking a skill). Also, shootouts are ignored.

The 2009-10 Leafs were dead last in the league in both PP and PK, and had Toskala/Gustavsson in net to boot. So the reason they could come in 29th when they had a high Corsi is because they were downright awful at all the aspects of the game not covered by Corsi.

It's fairly well known that having great goaltending can "cheat" Corsi - see 2010 Habs, 2011 Bruins, 2012 Predators.

People were actually claiming that?

Or is this another case of "over a large enough sample we assume it evens out" so that it can be ignored? (since it can't be objectively measured at the moment)

Shots definitely come in different qualities, and most statistical analysts have identified that:

A) shot quality is higher when a team is on the power play, because there are more cross-ice passes and back-door plays that make life difficult for goalies.
B) teams take better-quality shots when they are ahead (because the other team is taking more chances) and lower-quality shots when they are behind (because the other team is retreating into a defensive shell).

Analysts generally have decided to consider special teams a completely separate aspect of the game (limiting Corsi and Fenwick to measurements of even-strength play) to account for A, and have developed formulas to take score situations into account to account for B (for an example see here: http://www.broadstreethockey.com/2012/1/23/2722089/score-adjusted-fenwick).

But aside from those two relatively simple factors, shot quality is just considered too subjective to be factored into calculations. So essentially, we're just going to have to live with an imperfect system. Current Fenwick stats still give a pretty good picture of what is going on for most teams, despite the imperfections. (For example, the Hawks and Bruins showed up near the top of most shot-based stats last season, and the Sharks are currently #1 in Fenwick).

I'm not very clear on how all the advanced stats work and what they represent but I'm curious as to why shot quality is not considered a legit thing.

Is it because it's difficult to qualify or what?

How is a shot from centre or from the corner equal to a point blank shot from the slot?

Surely people recognize that not all shots are created equal.

It's just difficult to figure out how "good" a shot is without having game tape in front of you. The only thing you can really do is work with shot locations, and even that is pretty tedious. So for the most part, people just ignore shot quality and accept that the system isn't perfect.

In the case of the Leafs, the blog Pension Plan Puppets actually did a series of posts over the off-season which showed that the Leafs weren't particularly good at keeping shots out of prime scoring areas last season. So in other words, even accounting for shot location wouldn't change the fact that the Leafs were getting outplayed on a regular basis.
 
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Gutchecktime

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Dec 24, 2005
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The Leafs are playing a very unsustainable brand of hockey. It is actually very mindboggling that they've accumulated these many wins over the past season and thus far.

At what point do you stop calling something unsustainable though and start investigating how it's been sustained? Serious question. The Leafs have been "outpossessed" in 43 of their last 55 games going back to the first game of last season. In those games, they're playing at a 113 point pace. How many games do they have to play a "playoff level point pace" before we start taking a look at how they're able to overcome lack of possession instead of chalking it up to just "luck"?

Is it 60 games of being outpossessed and still competitive? 82 games of being outpossessed and still competitive?... 43 games of being outpossessed and playing at that high of a level already has me a little intrigued. They're under .500 when they "outpossess" their opponents.
 

Rants Mulliniks

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Jun 22, 2008
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Corsi and Fenwick measure the effectiveness of a team's skaters at even strength. It does not cover goaltending or special teams (and Corsi doesn't even consider shot blocking a skill). Also, shootouts are ignored.

The 2009-10 Leafs were dead last in the league in both PP and PK, and had Toskala/Gustavsson in net to boot. So the reason they could come in 29th when they had a high Corsi is because they were downright awful at all the aspects of the game not covered by Corsi.

As I said "there are certain things that are far more relevant to the outcome."

Why would it surprise people that a team that is 3rd in PK, 3rd in PP, 9th in SV %, 4th in goals per game and 7th in goals against per game and regularly gives up shots in low percentage areas while taking shots in high percentage areas is successful?
 

Machinae

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Jul 6, 2007
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Mississauga, ON
I chalk up the Leaf's success so far to good goaltending and a very potent counter attack with multiple threats able to score off the rush. Their defense is able to keep shots to the outside despite losing board battles and being out cycled in their own zone constantly. The forward lines, outside of a few forwards (mostly McClement) are horrible at winning possession along the boards and cycling the puck, much like the defense.

Oh oh, we fight, it gives momentum! :sarcasm:
 

Garbs

Registered User
Jul 2, 2005
15,212
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London, Ontario
It's easy to see just watching a few Leafs games that they are in their own end waaay too much. It's easy to see watching a few Leaf games that their goalies have been quite good.

The real reason they have been able to get away with their poor Corsi et all is their PP. That's what has saved them so far.

It's not unusual for special teams to make a team look a lot better early on but that typically flatlines. There is a lot of hockey to be played. I don't get why Leaf fans are so defensive. Enjoy the little run.

We had the 14th ranked power play last season.

What saved us then?
 

Freudian

Clearly deranged
Jul 3, 2003
50,414
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I'm not very clear on how all the advanced stats work and what they represent but I'm curious as to why shot quality is not considered a legit thing.

Is it because it's difficult to qualify or what?

How is a shot from centre or from the corner equal to a point blank shot from the slot?

Surely people recognize that not all shots are created equal.

No one records shot quality. The only reason shot attempts is the main stat used is that it's tracked. Not because it's particularly good to use.

I realize there have been some shallow attempts to prove that shot quality doesn't matter, but that's not particularly convincing. But if all you have is shot attempt based stats you feel the need to show that's good enough.

Proper tracking of the puck and players would revolutionize hockey analytics. But until then people have to settle trying to squeeze the stats that are tracked into formulas with rather weak explanatory power.
 

Tyler Biggs*

Guest
I'm not even concerned about the amount of shots the Leafs give up. Most are easy shots from the perimeter. Although the Leafs only had 14 shots, 10 of them were dangerous. This team can generate some serious offense. Can't wait to see this team with Clarkson and Kulemin on it.

Wasn't the pp's the Leafs got, Minny had more. Never had that many shots, but four went in the net. Don't matter how many shots you throw at the net, if you can't put them in the net it means squat.
 

Tyler Biggs*

Guest
Enough with this 'Leafs are lucky' garbage. So they got only 14 shots and gave up 37, did you see the goals? Tic tac toe and such. They get quality scoring chances and capitalize on them, and minus those breakaways they give up low quality chances and perimeter shots.

A win is a win baby. GLG!
 

Reznor

Registered User
Feb 20, 2013
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Fribourg
I'm not very clear on how all the advanced stats work and what they represent but I'm curious as to why shot quality is not considered a legit thing.

Is it because it's difficult to qualify or what?

How is a shot from centre or from the corner equal to a point blank shot from the slot?

Surely people recognize that not all shots are created equal.

A quite good article to explain the basics of Corsi/Fenwick
http://www.grantland.com/blog/the-t...the-fakers-guide-to-advanced-stats-in-the-nhl
And that's for Corsi and the Leafs
http://www.grantland.com/story/_/id/9799967/toronto-maple-leafs-advanced-stats
 
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Fourier

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Dec 29, 2006
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Waterloo Ontario
To CORSI, perhaps. Not to "advanced" stats in general.

Besides, if you've paid attention to me long enough, you know that I hate the term "advanced stats". There's nothing particularly advanced about addition, subtraction, multiplication, and division. We're not splitting the atom here. We're not curing cancer. It's a game.
But what if you do lots of that stuff all at the same time? :D

BTW, having watched about 2/3 of the Leafs games and all of the Oilers games I'd say these two teams show the value of good goaltending. If you flip goalies these two teams probably flip records as well. The Oilers goaltending this year has been the worst I have seen in all my days as a fan of the team and I go back to '72. The Leafs on the other hand have had great goaltending when they needed it. I . don't consider this luck though. That is exactly what the goalie is suppose to do
 
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Morbo

The Annihilator
Jan 14, 2003
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Toronto
But what if you do lots of that stuff all at the same time? :D

BTW, having watched about 2/3 of the Leafs games and all of the Oilers games I'd say these two teams show the value of good goaltending. If you flip goalies these two teams probably flip records as well. The Oilers goaltending this year has been the worst I have seen in all my days as a fan of the team and I go back to '72. The Leafs on the other hand have had great goaltending when they needed it. I . don't consider this luck though. That is exactly what the goalie is suppose to do

Are you trying to say the only difference between the teams is goaltending? Really?
 

Master_Of_Districts

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Apr 9, 2007
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It's not the Leafs winning 6 games. It was like this all last season too. Going back to Carlyle's time with the Ducks they were similar as well. The difference is that under Martin the Habs were one of the best defensive teams in the league. No such accolades for the Leafs. They are nowhere near the level of defense that Martin's Habs were. Also under Therrien the Habs didn't play off the rush like the Leafs do, they peppered the goalie with shots til they scored. In fact there really is no comparison to made lol.

You're wrong.

05-06 ANA - 52.4% shot percentage (no data on missed shots) at EV; made playoffs

06-07 ANA - 53.4% shot percentage (no data on missed shots) at EV; made playoffs

07-08 ANA - 50.4% 5-on-5 Fenwick; made playoffs

08-09 ANA - 50.5% 5-on-5 Fenwick; made playoffs

09-10 ANA - 46.8% 5-on-5 Fenwick; missed playoffs

10-11 ANA - 45.1% 5-on-5 Fenwick; made playoffs (but outscored by 20(!!) goals 5-on-5)

11-12 ANA - Fired after Game 24; 40% 5-on-5 goal percentage; 0.458 5-on-5 Shot percentage

12-13 TOR - 44.0% 5-on-5 Fenwick; Made playoffs
 

Bear of Bad News

Your Third or Fourth Favorite HFBoards Admin
Sep 27, 2005
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Who exactly claims this?

That was actually the initial intent of the Corsi statistic, as developed by Jim Corsi. He wanted to measure everything that caused goaltender activity (which is why things like missed shots are counted, since the goaltender still has to react to them).
 

Ace88*

Guest
You're wrong.

05-06 ANA - 52.4% shot percentage (no data on missed shots) at EV; made playoffs

06-07 ANA - 53.4% shot percentage (no data on missed shots) at EV; made playoffs

07-08 ANA - 50.4% 5-on-5 Fenwick; made playoffs

08-09 ANA - 50.5% 5-on-5 Fenwick; made playoffs

09-10 ANA - 46.8% 5-on-5 Fenwick; missed playoffs

10-11 ANA - 45.1% 5-on-5 Fenwick; made playoffs (but outscored by 20(!!) goals 5-on-5)

11-12 ANA - Fired after Game 24; 40% 5-on-5 goal percentage; 0.458 5-on-5 Shot percentage

12-13 TOR - 44.0% 5-on-5 Fenwick; Made playoffs


That doesn't indicate anything.
 
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decma

Registered User
Feb 6, 2013
743
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We had the 14th ranked power play last season.

What saved us then?

I took a shot at this in post #12 above - while their PP% might not have been great, they scored many more PPG than their opposition did. Also more 4 on 4 goals. The vast majority of their positive goal differential came from these situations, not 5 on 5:

... how much does the Leaf's success in non 5-on-5 situations explain their overall success despite the 44.1% 5-on-5 Corsi? A quick glance at the NHL team goals for and goals against stats pages shows that their goal differential was a relatively pedestrian +5 (105 vs 100) in 5-on-5, but an impressive +12 (31-19) in PP situations, and +2 (3-1) in 4-on-4 situations.

In other words, 5 on 5 they scored 5% more goals than the opposition, but 5 on 4, 5 on 3, 4 on 3, and 4 on 4 they scored 70% more goals than the opposition (34 to 20). In actual goals instead of percentages, they were plus 5 in the former situation and plus 14 in the latter.

That impressive non 5-on-5 performance probably goes a long way in explaining their success, leaving less to be explained by 5 on 5 luck vs. 5 on 5 quality shot skill.
 

Feed Me A Stray Cat

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Mar 27, 2005
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Boston, MA
At what point do you stop calling something unsustainable though and start investigating how it's been sustained? Serious question. The Leafs have been "outpossessed" in 43 of their last 55 games going back to the first game of last season. In those games, they're playing at a 113 point pace. How many games do they have to play a "playoff level point pace" before we start taking a look at how they're able to overcome lack of possession instead of chalking it up to just "luck"?

Is it 60 games of being outpossessed and still competitive? 82 games of being outpossessed and still competitive?... 43 games of being outpossessed and playing at that high of a level already has me a little intrigued. They're under .500 when they "outpossess" their opponents.

Since the lockout no team has been able to sustain this type of even strength shooting percentage.

There's no set rule, but I want to see the Leafs do this for two seasons before claiming they're the only team in the past decade able to shoot this well.

We have zero samples of a team like Toronto over multiple seasons. We have examples of teams like the 09-10 Capitals regressing to the mean in regards of shooting, though.
 

hatterson

Registered User
Apr 12, 2010
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North Tonawanda, NY
No one records shot quality. The only reason shot attempts is the main stat used is that it's tracked. Not because it's particularly good to use.

I realize there have been some shallow attempts to prove that shot quality doesn't matter, but that's not particularly convincing. But if all you have is shot attempt based stats you feel the need to show that's good enough.

Proper tracking of the puck and players would revolutionize hockey analytics. But until then people have to settle trying to squeeze the stats that are tracked into formulas with rather weak explanatory power.

I would *love* to see the type of tracking system that some basketball teams are using.

http://www.grantland.com/story/_/id...ors-sportvu-cameras-nba-analytical-revolution

Obviously there's some more technical issues because a puck is harder to track than a basketball, but something like this would be an absolute *goldmine* of data for us to use, especially when looking at shot quality.

eg, A one timer from a fast cross-ice pass with a screen in front is far more dangerous than a normal slapper with zero movement and traffic, but we don't have access to that now.

On the topic of this thread, it would let us know several answers. Or at least give us a better way to approach them. Are the Leafs really shooting better than every other team in the league has been able to in recent history (Either caused by luck or absurd skill)? Or are they just taking better shots than everyone else?
 

Bear of Bad News

Your Third or Fourth Favorite HFBoards Admin
Sep 27, 2005
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I agree - that level of tracking would be the Holy Grail of hockey analysis.
 

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