Zone starts and impact on players statistics

The other day on twitter I was called out by Sam Ventura who does some great work on war-on-ice.com. Specifically he did not like my article on zone starts that I wrote the other day.

Let me step in here and say that I have never denied this. Offensive zone face offs are more likely to result in shots for the team on offense and less likely for the team on defense. Ok, that is settled, lets move on.

 

This is the crux of the problem. At the micro level yes, the location of face offs impacts outcomes. On the macro or aggregate level they are minimal. I tried to explain that here in more detail but maybe it didn’t come across too well so I will try again, in another way, with the war-on-ice tools. Let’s look at the Shea Weber picture from above Sam’s tweets above.

Weber1

Ok, do there looks like a relationship. The higher the offensive zone start percentage the higher the CF%. Now, let’s take a look at the same chart but Offensive zone start percentage relative and see how the chart changes.

weber2

Significantly less correlation. Why? Because when the team is playing well the team as a whole generates more offensive zone starts. Not the other way around. We can also flip it around and look at how ZSO% compares to CF%Rel.

Weber3

And to finish the display we can look at ZSO%Rel vs CF%Rel.

Weber4

The relationship that Sam has observed is largely team driven, not Weber’s zone starts driven. There is a zone start impact on a players statistics but it is very minimal and for the majority of players can safely be ignored. The impact of the team is far more important. When the team does well it will result in a better CF% which in turn results in a higher ZSO% which is the reason for the high correlation. Zone starts don’t drive CF%, CF% drives zone starts. This makes total sense because the majority of zone starts will come after a shot on goal. The shot on goal produces the offensive zone face off, it isn’t the offensive zone face off that produces the shot on goal. We need to think of zone starts more as a result, not a cause.

On top of the team effect, I believe there is a style of play impact too which will take away even more correlation. When you play defensive hockey you often give up more shots. We see it in score effects all the time. Players who start more in the defensive zone are more likely to be the ones playing defensive hockey. This adds to the correlation as well and has nothing to do with zone starts.

Let me leave you with Phaneuf’s charts because his correlation in Sam’s charts was probably the greatest.

 

 

Phaneuf1

Phaneuf2b

Again, a significant portion of the relationship disappears when you look at ZSO%Rel.

For me, the main evidence that zone starts don’t have a significant effect on a player’s overall statistics is if I remove the 45seconds after all offensive/defensive zone face offs (which basically ignores the entire shift) the majority of players have the same CF% +/- 1% and only a handful with heavy offensive or defensive zone starts have an effect in the +/- 1-2%. If removing all shifts that start with an offensive or defensive zone start does not dramatically impact a players overall statistics you simply cannot conclude that zone start bias plays a prominent role in driving a players overall statistics. Yes, for a particular shift it will, but not overall. Furthermore, the majority of that impact occurs in the first 10 seconds after a face off which is why my zone start adjusted data removes these 10 seconds which is something I showed over 3 years ago.

The critical point to remember in all of this is shots drive where face offs occur, where face offs occur do not drive shots. Coaching and line changes for face offs can impact overall player statistics a little but really not all that much.

 

2 comments

  • I agree with you generally that Zone Starts have little impact in aggregate, but I do think that they do have a significant impact in small samples and I’m not sure that your data here refutes that.

    When you say: “if I remove the 45seconds after all offensive/defensive zone face offs (which basically ignores the entire shift) the majority of players have the same CF% +/- 1% and only a handful with heavy offensive or defensive zone starts have an effect in the +/- 1-2%” it doesn’t really test whether zone starts have an effect on possession, because most players in your sample are going to have fairly similar zone starts in total.

    I think a good test would be if you removed the 45 seconds following only offensive faceoffs (or defensive I suppose, just not both) and see if the change is still small. I suspect based on what I’ve seen that you’ll see much larger deltas, but I’m not 100% sure if this test will align with what I looked at.

  • Hey David,

    Just wanted to say that I agree with you completely, zone starts really aren’t that meaningful to the ultimate outcome. Whether that means a shot attempt or a goal. It’s something like only 1 in every 3 offensive zone starts directly results in a shot attempt and I think people over-estimate the importance.

    I have my own blog post on it, which I just finished when I saw this one.

    http://xtrahockeystats.com/wordpress/?p=17

    My stats page is still a work in progress but i can be accessed by just deleting the wordpress part.

    Keep up the good work.

    Nick