Busting an NHL myth: 'The best teams block the most shots'
by James Mirtle on Dec 1, 2008 5:15 AM CST
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"It’s become a new thing in the N.H.L. It’s a very good defensive tactic. You hear a lot of coaches say, ‘Get in the shooting lanes.’ We do our penalty-killing meetings, talk about defensive-zone coverage, and they always talk about getting in the lanes."
It seems to me we've heard more and more about blocking shots the past few years, and the stat is often attributed to the best defensive players — and teams — when it comes to evaluating their play in their own end.
Looking at the stats, however, it's not hard to see that a team like Detroit, for example, is consistently near the bottom of the NHL in shot blocks, and is this season right in dead last. The Islanders, meanwhile, lead with 17.7 blocks per game, almost exactly double the Red Wings, and are (needless to say) trailing them in the standings.
Probably the best way to look at how shot blocking relates to other measures of how good teams are is to look at the statistical correlation between blocks per game and a whole bunch of other common metrics. Does blocking more shots, for example, mean your team is also strong at penalty killing, preventing goals or preventing shots against?
Is Detroit an anomaly or do the league's other good teams get in the way of pucks more than those on the low end?
(As a brief aside, when it comes to the basics of correlations, 1.0 equals a high degree of correlation and -1.0 equals a negative correlation. A really high figure would be something like wins compared to points percentage, which has a direct relationship and a correlation of .936 this season. Goals against and points percentage, meanwhile, has a fairly strong negative correlation of -.60.)
Figures like goals for are very strong indicators of how good a team is in the standings (points percentage). Blocking shots (SB/G), however, is by my calculations on the wrong end in that regard:
I hope that's clear enough.
Basically what the chart shows is that, in relation to points percentage, goals per game is the highest metric in terms of correlation at .70 followed by 5-on-5 goal differential. Goals against per game is obviously negatively affecting teams' ability to point up points, as is shots against per game (albeit not as significantly).
Here's the data for the stat heads out there:
| P% | G/G | GA/G | 5-5 F/A | PP% | PK% | S/G | SA/G | SH% | SV% | SH+SV | SB/G | |
| P% | 1.00 | |||||||||||
| G/G | 0.70 | 1.00 | ||||||||||
| GA/G | -0.60 | 0.00 | 1.00 | |||||||||
| 5-5 F/A | 0.64 | 0.55 | -0.48 | 1.00 | ||||||||
| PP% | 0.46 | 0.55 | -0.08 | 0.06 | 1.00 | |||||||
| PK% | 0.38 | -0.07 | -0.62 | -0.15 | 0.20 | 1.00 | ||||||
| S/G | 0.54 | 0.44 | -0.11 | 0.26 | 0.30 | 0.07 | 1.00 | |||||
| SA/G | -0.34 | -0.36 | 0.04 | -0.04 | -0.11 | -0.12 | -0.37 | 1.00 | ||||
| SH% | 0.38 | 0.76 | 0.08 | 0.41 | 0.37 | -0.12 | -0.24 | -0.13 | 1.00 | |||
| SV% | 0.35 | -0.18 | -0.85 | 0.39 | 0.02 | 0.48 | -0.10 | 0.49 | -0.12 | 1.00 | ||
| SH+SV | 0.54 | 0.34 | -0.67 | 0.60 | 0.26 | 0.33 | -0.24 | 0.34 | 0.54 | 0.77 | 1.00 | |
| SB/G | -0.31 | -0.31 | -0.02 | -0.27 | -0.33 | 0.03 | -0.30 | 0.17 | -0.12 | 0.12 | 0.02 | 1.00 |
Shot blocks per game comes in at -.31 in relation to both points percentage and goals for per game, meaning that there's a small correlation between teams that are putting up goals and points and a low figure in blocking shots.
Having a lot of shot blocks has zero relationship with goals against and penalty killing percentage, and has a very, very slightly positive relationship with save percentage.
Good teams that don't shot block (.600+ points percentage): Detroit, Calgary, Anaheim, NY Rangers, San Jose, Washington
Bad teams that block a lot of shots (-.500): N.Y. Islanders, Colorado, Ottawa, Phoenix, Toronto
My theory is that this means that teams that (a) spend more time penalty killing, (b) spend more time in their own end, and (c) simply lack the speed and/or finesse to defend in other manners all rely more on blocking shots. If you're a puck possession team like Detroit or Washington, are you lying down in front of shots or stick checking? Is there a relationship there? Does speed and positioning trump the block?
(Nick Lidstrom, for example, won the Norris Trophy and was ranked 132nd last year in shot blocks by defencemen, behind Dick Tarnstrom and Freddy Meyer, among others.)
That said, there are teams that go the other way, too.
Good teams that shot block: Montreal, Pittsburgh
Bad teams that don't shot block: Dallas, Atlanta
Bloggers like Tyler Dellow, Five Hole Fanatics and The Falconer have been doing some nice work with correlations and hockey stats for a while now, and it's something I'd like to integrate here more often. It's interesting, to me anyway, that something like shots per game has a higher correlation with points percentage this season than things like power play percentage and save percentage.
There's also a correlation there between the number of shots a team allows and how high its save percentage is, which is interesting.
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Just a little more explanation ...
(Because correlation can be confusing, as I know from teaching stats a few times …)
First, remember that just because two variables are correlated does not mean that changes in one cause changes in another (this was not implied in the post, but is a very common misunderstanding).
A correlation of 0 means that two parameters have no relationship at all. A small absolute value indicates a weak correlation, and the closer it is to 1.0 the stronger the relationship between the two parameters. A negative correlation does not imply a weak correlation or any kind of “value judgement” – it simply means that as one parameter varies in one direction, the other parameter varies in a negative direction, while a positive correlation indicates that the two parameters vary in the same direction. As one increases, so does the other. (And I’m not even going to mention statistical significance this early in the morning!) :)
Interesting stuff.
"A vacuum is a hell of a lot better than some of the stuff that nature replaces it with." -- Tennessee Williams
by Baroque on Dec 1, 2008 6:23 AM CST reply actions 0 recs
Thanks Baroque… I’m unearthing this stuff from the cobwebs of my brain so if I err with any of the terminology, let me know.
by James Mirtle on Dec 1, 2008 12:56 PM CST up reply actions 0 recs
No problem. It’s been a few years, but some things just stick in your brain like an alien parasite, no matter how hard you try to get them out. :)
"A vacuum is a hell of a lot better than some of the stuff that nature replaces it with." -- Tennessee Williams
by Baroque on Dec 1, 2008 5:06 PM CST up reply actions 0 recs
A nice sort of rhyme to remind us of this fact:
Correlation does not equal causation.
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by Chemmy on Dec 1, 2008 2:14 PM CST up reply actions 0 recs
Oooohhhhhhhhhh!!!!!! A correlation matrix! I love it.
There’s some very interesting stuff in here, quite aside from shot blocking. Some of it cries out for a deeper look. I’d love to know if there is a good explanation as to why there is a negative correlation between shots allowed and goals scored, while there’s almost a zero correlation between shots allowed and goals allowed. That seems very counterintuitive, but there is also a significant positive correlation between shots allowed and save percentage.
Do teams that allow more shots just have better goalies? If so, is that because GMs recognize that their team needs a better goalie, or that coaches recognize that they can allow a system that gives up more shots because they have a better goalie? Or, is it because teams that give up a lot of shots tend to give up poorer quality shots? If you know that you can penetrate a defense and get a better shot, do you take fewer of them? Or is it something else? Or random chance?
Shots taken has stronger correlations to both scoring goals and preventing goals than does shots allowed. Going out on a limb, this suggests to me that the real difference between the caliber of teams is offense, and that there is a much narrower range of team’s ability to play defense. Is this support for the idea that it is easier to play good defense than good offense?
by J. Michael Neal on Dec 1, 2008 6:39 AM CST reply actions 0 recs
James, quick question; is the data behind your matrix for this season only? I’ve done similar for seasons past and will have to compare to see if any significant differences pop up.
by Dirk Hoag on Dec 1, 2008 6:51 AM CST reply actions 0 recs
Yes, this is from this season only — however, I did check the SB/G vs. Points% figures for the previous two seasons and they were nearly identical.
Some of the other correlations fluctuated.
by James Mirtle on Dec 1, 2008 12:57 PM CST up reply actions 0 recs
good teams don't need to block a lot of shots
As a amateur hockey coach I can tell you why some good teams don’t block many shots. If the puck is in your offensive end you won’t get too many opportunities to block shots. For example, my team played a game yesterday afternoon and had a 40-8 shot advantage. We don’t keep track of blocked shots but which team would likely have an advantage in that statistical area?
by Pseudonym on Dec 1, 2008 9:25 AM CST reply actions 0 recs
Veeery interesting
I’d never had the impression that blocking a lot of shots in total is a good thing. Knowing and being willing to block shots when appropriate is good, but the volume itself says to me you’re just giving up too many shots and possessing the puck too little. Detroit at the low end makes perfect sense with how good they are and the style they play.
That Shanahan quote is funny. I wouldn’t say blocking shots is “the new thing,” but (particularly if coaches increasingly emphasize it) perhaps it would qualify as “the new trap” — i.e. a tactic for underskilled teams who don’t have the puck as much to try to decrease goals against. I certainly get the impression the Islanders block a lot out of necessity rather than belief that it is the way to the prize (and coincidentally, they have a few players who are very willing to do it).
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by Dominik on Dec 1, 2008 9:52 AM CST reply actions 0 recs
This is a tactic that gained a lot of traction in lieu of the Carolina/Edmonton SCF. Both teams were heavy shot blockers. One was an 8th place team that made a run, the other had a no name defence but was a top seed.
Montreal is a pretty lousy team defenisvely, mainly due to the forwards if you ask me. It’s no secret that Montreal relies heavily on shot blocking and good goaltending for their defensive success… they never have a very good shot differential and are often outshot. Their save percentage to shooting percentage ratio last year shed way more light into the big GF/GA differential than the shots for and against did.
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by saskhab on Dec 1, 2008 10:15 AM CST reply actions 0 recs
This is a terrific post.
Re: Puck possession teams like DET and WSH… The Caps have been awful at puck possession the last few games because injuries have forced them into playing 3+ AHL D. In the last two games the Caps have 10 and 14 blocked shots, well ahead of their season average of about ~6/game.
by TylerG on Dec 1, 2008 10:18 AM CST reply actions 0 recs
Great post
Mr. Mirtle. Shot blocking is definitely overrated.
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by eyebleaf on Dec 1, 2008 10:27 AM CST reply actions 0 recs
I did my own post on the subject a little while ago. I corrected for puck possession by looking at percentage of shots blocked (blocked shots/blocked shots+shots on net):
Detroit, for example, only blocked 9.6 shots/game while about 33.16 shots were being directed at their net every night (blocked shots+shots against). Calgary, on the other hand, blocked slightly more shots per game (9.9), but mainly because they had more pucks flying around at the bad end of the ice (38.41). So while the Wings blocked less shots on average, we can probably say they were better at it than the Flames were (29% of total versus 26% of total).
by Kent Wilson on Dec 1, 2008 10:27 AM CST reply actions 0 recs
Yeah, I think you would need to look at the correlation between [blocked shots/(blocked shots+shots on net)] and P% instead of just the raw total of blocked shots.
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by marcello on Dec 1, 2008 3:11 PM CST up reply actions 0 recs
Keep in mind that there’s not really much of a correlation between blocked shots and shots against, so the teams goalies getting shelled aren’t necessarily the ones dropping in front of a lot of pucks as well.
The bottom teams in the league in ‘shot blocks + shots against’ are Detroit and San Jose, two of the strongest clubs.
by James Mirtle on Dec 1, 2008 3:56 PM CST up reply actions 0 recs
That’s a good point.
When I was a kid I used to pray every night for a new bicycle. Then I realized God doesn’t work that way, so I stole one and prayed for forgiveness. - Emo Philips
Neglectful father of David Quinowski
by marcello on Dec 1, 2008 4:20 PM CST up reply actions 0 recs
However the correlation between SB/G and SA/G is still fairly low. It is the mostly highly positively correlated relationship for SB/G but it is still low. I’d like to see the how the ratio relates/percantage relates. I don’t expect much change but it might be enlightening.
by Mogen_david on Dec 1, 2008 4:49 PM CST up reply actions 0 recs
Just ran it. -0.17. And MON is blocking the highest percentage of shots at net (not including misses).
by Mogen_david on Dec 1, 2008 5:25 PM CST up reply actions 0 recs
Adding to this I just ran Blocked shots controling for G/G and GA/G and found no relationship for either BS/G or BS/(BS+SH).
by Mogen_david on Dec 1, 2008 6:10 PM CST up reply actions 0 recs
I was going to comment, but what kent says is exactly what I had in mind.
by Owen_ on Dec 1, 2008 11:25 AM CST reply actions 0 recs
SB/G and GA/G, PK%
Perhaps one of the more interesting things I found (aside from what was already mentioned) is to take the shot blocking stat one step further – is it correlated to a reduced goals against average or increased penalty kill percentage?
Notice the correlation of SB/G to GA/G: -0.02
And to PK%: 0.03
Shot blocks per game has almost no correlation to the amount of goals a team lets in, or its percentage of killing penalties. Very interesting, since the whole point of blocking shots is to stop goals from going in the net.
by jameshstephenson on Dec 1, 2008 12:36 PM CST reply actions 0 recs
I know… who would have thought? Keep in mind that I’m relying on a pretty small sample size (this season) and it would be worth looking at much more data to ensure that’s been a long-term trend.
by James Mirtle on Dec 1, 2008 1:05 PM CST up reply actions 0 recs
As a Leafs fan, last year under Maurice they didn’t block a lot of shots, and this year under Wilson they are blocking a lot of shots.
There have been a ton of goals this year that have ricocheted off Toronto defenders’ shin guards that probably would have been saved if allowed to travel on a straight line.
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by Chemmy on Dec 1, 2008 2:16 PM CST reply actions 0 recs
That’s part of the reason I’ve got shot blocking on the brain, I think. I put together that piece on the Leafs goaltending last week, and a lot of the feedback from readers was saying how the defence was playing so much different under Wilson, collapsing at the net and blocking shots and it was making things more difficult for Toskala.
by James Mirtle on Dec 1, 2008 2:24 PM CST up reply actions 0 recs
I’ve long been of the opinion that shot blocking is overrated. Injuries from it aren’t that common, but I’d bet that they offset a lot of the advantage of extensive shot blocking.
by J. Michael Neal on Dec 1, 2008 2:58 PM CST reply actions 0 recs
Good post
I was wondering the same as J. Michael, whether the injuries are worth all the bother.
But I have my own Q: Given that “today’s goalies are the best-conditioned, most-athletic, most-skilled ever” (note the use of ironic quotation marks), why are skaters blocking shots at all? If goalies are that good, shouldn’t skaters just get out of the way? Maybe tie up sticks to prevent deflections and rebound goals. But why block shots if “the worst goalies today are better than the best goalies 20 years ago” (this isn’t aimed at you, James; the myopic know who they are). Maybe what skaters should be doing is getting the hlll out of shooting lanes.
While I’m here: any data on the correlation between winning faceoffs and winning hockey games? Game analysts can’t shut up about it, but I wonder.
by Dr Van Nostrum on Dec 1, 2008 3:27 PM CST reply actions 0 recs
I think it’s pretty obvious why so many people praise shot blocking, and it isn’t because it’s effective at preventing goals. (It may or may not be so effective; I just don’t believe that’s the source of conventional wisdom.) Blocking shots is a sign of toughness, and willingness to sacrifice one’s body for the team. It’s virtuous. It’s like the center fielder (Fred Lynn, Andy van Slyke) who dives to make every catch he can. It may be stupid from a cost/benefit analysis (it certainly shortened Lynn’s career), but it shows guts.
Me, I’ll take Devon White. He didn’t bother diving to make catches most of the time. He just loped under it and caught it on his feet.
by J. Michael Neal on Dec 1, 2008 3:54 PM CST up reply actions 0 recs
If goalies are that good, shouldn’t skaters just get out of the way? Maybe tie up sticks to prevent deflections and rebound goals.
Dom Hasek hated his teammates getting in the way. He wanted them to do just that – clear out so he could see the trajectory of the shot clearly, and then after he made the first save and was flopping around like a twitchy fish out of water grab the rebound and clear it away, but don’t screen him and don’t deflect pucks on the way to the net so they change direction. Maybe it depends in part on how a goaltender played when he was younger – if he had a team that stayed out of the way, he got used to it, and that is the way he is most comfortable playing.
"A vacuum is a hell of a lot better than some of the stuff that nature replaces it with." -- Tennessee Williams
by Baroque on Dec 1, 2008 5:11 PM CST up reply actions 0 recs
my guess is that different goalies have different preferences as far as this goes…
by Ebscer on Dec 2, 2008 11:30 PM CST up reply actions 0 recs
> anova(lm(P.~FO.G.GGA.G))
Analysis of Variance Table
Response: P.
Df Sum Sq Mean Sq F value Pr(>F)
FO. 1 0.063868 0.063868 34.783 3.207e-06 *
G.G 1 0.112323 0.112323 61.171 2.695e-08 *
GA.G 1 0.117227 0.117227 63.842 1.811e-08 *
Residuals 26 0.047742 0.001836
—-
Signif. codes: 0 ‘’ 0.001 ‘’ 0.01 ‘’ 0.05 ‘.’ 0.1 ‘ ’ 1
or the correlation for FO% and P% is 0.43
Sorry for the R dump but I’m just running something quick and dirty.
by Mogen_david on Dec 1, 2008 6:23 PM CST up reply actions 0 recs
Interesting, when I pick at it a bit more FO% is only mildly predictive of P% and when exploring interactions shows no significance unless it interacted with G/G. A hint of offensive zone face of wins? Not sure. Back to work.
by Mogen_david on Dec 1, 2008 6:36 PM CST up reply actions 0 recs
One thing to note James is the quote you lead with is about being in the lane not blocking shots. How many shots aren’t taken because the lane isn’t open for the shot.
by Mogen_david on Dec 1, 2008 4:42 PM CST reply actions 0 recs
He’s talking about shot blocking, though. That’s what the NYT piece is all about.
by James Mirtle on Dec 1, 2008 4:49 PM CST up reply actions 0 recs
Well durn, here I thought I had an interesting point and you want me to go read the article.
by Mogen_david on Dec 1, 2008 4:52 PM CST up reply actions 0 recs
Your SA/G and SV% may be a mix of shot quality and evidence for the idea that goalies like to see at least some rubber to stay on their game. Should be a fun one to tease apart.
by Mogen_david on Dec 1, 2008 4:54 PM CST reply actions 0 recs
Does a deflection off the stick and out of play count as a blocked shot? Or is shot blocking just limited to body blocking?
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by saskhab on Dec 1, 2008 5:50 PM CST reply actions 0 recs
quality over quantity?
I was thinking if teams could block most or all the shots that normally be a shot on net it would be hard for teams to score and win. Maybe the low shot blocking teams are doing just that – blocking only shots that would be on net and not go out of position just to block a shot that would go wide.
...
by puckbuddy on Dec 1, 2008 7:27 PM CST reply actions 0 recs
Relationship between Shots Against Per Game and SV%
People who study Shot Quality SV% have pointed out the interaction between these two things. Teams with weak goaltenders have defensemen who try to prevent shots, while teams with better goaltending are more likely to just let their net minder stop the puck. So good netminders see more pucks which leads to more easy SV and a higher SV%. There is an interaction between quality of net minding and Shots Allowed.
I think the clearest example of this was the pre-lockout St. Louis Blues who had terrific defensemen (Pronger, MacInnis) and so-so net minders (Lalime, Turek). They often allowed the fewest SA per GP and yet their goalies had bad SV%. If you trust your goalie you less likely to drop down if it is a borderline situation.
by The Falconer on Dec 1, 2008 9:12 PM CST reply actions 0 recs
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