I have written a number of posts on zone starts and how they don’t generally have a significant impact on a players overall statistics but I constantly run across people that find that difficult to accept. There are still studies being done looking at how long the impact of a zone start has on outcomes (this was based on some of the work of Tyler Dellow). While these are interesting studies, the important thing to understand is that while there is an impact it has relatively little impact on a players overall statistics.
Before Tyler Dellow was hired by the Edmonton Oilers he suggested that my 10 seconds was not sufficient and like the article I linked to above he suggested the impact went on much longer though I could never pin down exactly what that number was. In my work I determined that after 10 seconds after a zone face off there is no noticeable impact on a players statistics and even the 10 second adjustment is minimal. I hope to try and explain why this is with this post.
The first significant fact to know is that when you remove the 10 seconds of play after all offensive and defensive zone face offs from a players 5v5 statistics you are removing approximately 15% of their ice time.
Now, let’s consider a hypothetical 50% corsi player during normal, non-face off influenced play. Now, for the 10 seconds after an offensive zone face off he is a 100% corsi player and for the 10 seconds after a defensive zone face off he is a 0% corsi player (these are the most extreme scenarios that in reality don’t happen).
Now, let’s also assume that the player is a 70% dzone face off player meaning that of all the offensive and defensive face offs he is on the ice for 70% of them are in the defensive zone and 30% are in the offensive zone. This is a pretty extreme zone start differential that only a handful of players get.
So now we have 85% of a players 5v5 ice time beyond the 10 seconds after a zone face off at 50% corsi. We have 4.5% of his ice time (30% of 15%) after an offensive zone face off with 100% corsi and we have 10.5% of his ice time after a defensive zone face off with 0% corsi. Add that all up and his expected corsi is 50%*0.85 + 100%*0.045 + 0%*0.105 = 47%.
That means, for this extreme zone start player the maximum impact of the 10 seconds after a face off is a drop in his Corsi from 50% to 47%. In reality it would be less because corsi isn’t 100%/0% after for 10 seconds after an offensive/defensive face off but for the purposes of identify an upper bound on the impact this suffices.
Now, one might suggest that the impact of the zone start is more than 10 seconds which may be true. Remember though that the percentage of the players overall ice time that the second 10 seconds would account for would be less than the 15% of the first 10 seconds since there might be another face off or a line change. I don’t have that number off hand but let’s assume it is 8%. Furthermore, the impact on Corsi will be far less significant in that second 10 seconds. Corsi in that second 10 seconds is likely more like 65%/35% than 100%/0%. If the next 10 seconds accounted for 8% of his ice time with a 65%/35% ozone/dzone corsi it would drop his Corsi% from 47% to 46.5%, just an additional 0.5% which is pretty much within the range of noise. Beyond that the impact would be negligible.
Now, let’s do these same calculations for a guy who has 60% defensive zone face offs and 40% offensive zone face offs which is far more common than 70/30. This player would have his 10 second impact take him from 50% corsi to 48.5% corsi. The following 10 seconds would see his corsi drop from 48.5% to 48.26%, just an additional quarter percent. The majority of players will be within this range (of all players with 500 5v5 minutes last season 87.4% were within 40-60% DZone%) and have a maximum potential impact of +/- 1.75%.
Let’s take a look at some of the players who had the most intense defensive zone starts from last season and see how their 5v5 stats compare with their 5v5 – 10s after a zone start stats (which I call F10 stats) to show the true impact.
|Player_Name||Dzone%||CF%||F10 CF%||CF%- F10CF%|
The biggest impact is just -2.8% (Marcus Kruger) and the average impact among these players is just -1.24%. This is well below my maximum impact estimates above so my theory is over estimating reality. The following scenarios might explain why.
Scenario 1: Player A is on the ice for a neutral zone face off which his team loses. The opposing team immediately goes on the offense and take a shot which the goalie saves driving it into the corner where the opposing team retrieves the puck and the goalie saves it and covers it up ending play. This would account for 2 shots against after a neutral zone face off, both of which Player A was on the ice for.
Scenario 2: Player A is on the ice for a neutral zone face off which his team loses. The opposing team immediately goes on the offense and takes a shot which the goalie saves and covers up the puck forcing a face off. Player A along with all his teammates remain on the ice for the defensive zone face off when his team again loses and the opposing team takes a shot which the goalie saves and covers again. This would account for 1 shot after a neutral zone face off and one shot after a defensive zone face off.
The reality is, both of these scenarios should be accounted for identically as it was losing the neutral zone face off and letting the opposing team enter their zone that resulted in both of these shots. The fact that there was a face off between shots doesn’t change that if the players didn’t change. We can’t be letting players off the hook just because his goalie covered up the puck and forced a face off in between shots. The reality is, when we count zone starts we should really only be counting face offs where the player was not on the ice prior to that face off. By not doing so we are not properly assigning credit/blame for some shots for/against. This is why in reality the impact is smaller than I calculated in theory.
Do zone starts matter? Yes, a bit for some of the more extreme zone start usage players. For the majority of players its hardly worth considering.