Let's talk about shot blocking

Cam Charron
May 29 2013 03:38PM

It's not that blocked shots aren't important, it's that the team with the most blocked shots isn't necessarily the best team at shot blocking—the team with the most blocked shots is often the one trying to clear the puck out of its own end. Like in that PK above. It's an excellent shift from Tyler Carroll, but I'd bet that Guelph would rather not be down 3-on-5 in that situation.

So a new statistic has popped up: "Percentage of shots blocked" and it's a little dicey as well. Generally speaking, it's just not good to block a lot of shots or to be in situations where you have to block a lot of shots. "Percentage of shots blocked" has been kicking around but I've seen no evidence that it's a repeatable statistic that correlates with winning.

Eric T. had several interesting tweets today. I'm trying only to copy-paste the relevant stuff, but go to his feed from the last 12 hours ever and you'll find some great stuff:

Now, why do you suppose that is? How come the defencemen that block the highest percentage of shots are much, much worse on paper than the defencemen that block the lowest percentage of shots?

This is something I kicked around last summer and may as well publish a few results. The answer is that if you flip it around, and measure the players that have the highest percentage of their own shots blocked, you'd find that it's almost exclusively defencemen.

I broke down a list of the 500 players who took the most shot attempts in 2011-2012 from Behind the Net. Of those 500 players, 187 were defencemen. Those defencemen had a shooting percentage of 4.0% while forwards had a shooting percentage of 10.1%.

So far, nothing interesting or mind-blowing. Everybody knows that forwards are better shooters than defencemen. They shoot from closer, they get more breakaway opportunities and far more scoring chances.

But if you break down "percentage of attempts blocked", all but one of the players outside a single standard deviation from the median was a forward: Blake Comeau had 34.1% of his attempts blocked.

Break it down:

  Shooting % % of Attempts Blocked
2+ standard deviations higher 3.8% 42.8%
1 standard deviation higher 3.9% 35.8%
With 1 standard deviation 9.2% 24.5%
1+ standard deviation lower 9.9% 15.8%

Conclusion? Shots that are blocked are generally coming from well out, from shooters who score less than 4% of the time anyway. You'd need to block 25 shots before saving a goal, all while hoping that you aren't screening your goaltender or deflecting a puck. I'm guessing that the players who get in shooting lanes for point shots to block them end up costing their teams more.

Perhaps we could break down the "percentage of attempts blocked" even further and look at "percentage of forward attempts blocked". I don't have the capability for that, but it seems like there's more value in looking at players who block shots closer to the net. Three or four times a game a shot from a good scoring area is blocked and we don't count it as a chance.

But perhaps somebody with some programming knowledge could...

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Cam Charron is a BC hockey fan that writes about hockey on many different websites including this one.
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#1 David Johnson
May 29 2013, 03:45PM
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Time permitting I could look into this tomorrow. What's a good cut off? Shots within 25 feet?

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#3 Louis Pomerantz
May 29 2013, 09:42PM
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Conclusion? Shots that are blocked are generally coming from well out, from shooters who score less than 4% of the time anyway. You'd need to block 25 shots before saving a goal, all while hoping that you aren't screening your goaltender or deflecting a puck. I'm guessing that the players who get in shooting lanes for point shots to block them end up costing their teams more.

One thing you may be forgetting is the amount of times those low percentage shots create rebounds that bounce directly into a prime scoring area that those high percentage shooters you speak of put into the back of the net. The example that comes off the top of my head would be lucic banging home a rebound created by chara's slap shot bouncing off reimer's pad for their third goal in their epic game 7 comeback. If that shot gets blocked, there is no opportunity for Lucic to gain possession of the puck in a prime scoring area with Rask down and out of position. Especially in power play situations when the attacking team is more capable of out numbering the defending team in front of the net, getting a puck through to the net is a good play in and of itself just so that the puck can be in a prime scoring area. There is likely biases in the samples of players that Eric T tweeted because players like Mark Fraser don't contribute in the ways that a Drew Doughty can, so for him to provide any contribution to his team he must be willing to throw his body in front of the puck. So by nature, worst players on average will be more willing to do the "dirty" work than the star players whose contributions are more obvious. Also, coaches could potentially tell their top players like a Chara not to try to block every shot because their too valuable to potentially lose over something that will likely be inconsequential anyway. Overall I do think that the percentage of shots a player blocks would likely be of some value, albeit it small, but I do not have any statistical analysis to back that up.

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#4 Eric T.
May 30 2013, 07:39AM
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@Louis Pomerantz

I agree with you that it's not simple enough for the shooting percentage alone to give us the answer.

But remember that a lot of blocked shots create rebounds too. (I'll counter your Lucic example with Girardi's blocked shot here: http://www.youtube.com/watch?v=bglKjZXiLyQ) And they create dangerous deflections too (from last night: http://www.youtube.com/watch?v=hMn_VgduU-Y). I think Cam is right to raise the question of whether it really works out to a positive value.

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#5 leafnerd
May 30 2013, 07:45AM
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I don't think you will be able to separate out "those" that shot block obsessively as a team strategy (rangers), those that shot block selectively and effectively without screening their goaling and the randomness of shot blocking which sometimes hits the player etc.

This will be a broad brush look at shot blocking but may not be applicable on the micro (player) level

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#6 Peachy
May 30 2013, 02:25PM
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Eric T. wrote:

I agree with you that it's not simple enough for the shooting percentage alone to give us the answer.

But remember that a lot of blocked shots create rebounds too. (I'll counter your Lucic example with Girardi's blocked shot here: http://www.youtube.com/watch?v=bglKjZXiLyQ) And they create dangerous deflections too (from last night: http://www.youtube.com/watch?v=hMn_VgduU-Y). I think Cam is right to raise the question of whether it really works out to a positive value.

Well, don't we know that shot blocking has positive value, if only because Fenwick is a better predictive statistic than Corsi is?

We can certainly argue about the degree of value shot blocking has, as well as the circumstances in which it has the most value, but I none of the evidence presented suggests that it necessarily has a negative value for the team.

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#7 Louis Pomerantz
May 30 2013, 02:58PM
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Very good point raised in the last comment by Peachy. It's possible that where the shot is being blocked has an impact on the value of the block. A block from a forward closer to the blue line may be more valuable than the block that Girardi made in Eric T. comment because that block came closer to the net and made it more likely it would bounce into a dangerous scoring area. Blocking a shot closer to the blue line would make it much less likely that it would bounce into a bad area. Also, any deflection or screen that results from the player trying to block the shot would be less detrimental on the goalie's ability to save it, if the block attempt is further away from the net.

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#8 Eric T.
May 30 2013, 03:15PM
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@Peachy

I don't think that proves it, no.

Fenwick has a higher long-run correlation to goals than Corsi does, but that may be because teams with a higher Fenwick than Corsi have kept the opponents' shots to the outside where they are more easily blocked, rather than because their players have tried harder to block them.

It might not even have anything to do with those shot blocks -- the causation chain could be:

1) Team keeps opponents farther from the net

2a) With fewer shots right near the net, the team gives up fewer goals

2b) With more shots from the point, the team blocks more shots and has a higher Fenwick than Corsi

This would lead to a higher long-run correlation between Fenwick and goals than Corsi and goals without any comment on whether those shot blocks added value. Blocking those point shots could be a net zero and still get the same results. It could even cost them goals, and as long as it cost them fewer than the reduction of scoring chances in 2a gained, we'd still find that Fenwick had a higher long-run correlation to goal scoring than Corsi did.

I think more likely than not, shot blocking will prove to have a small positive benefit. But I don't think the simple correlations of Fenwick and Corsi to goal scoring prove it.

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