Zone Start Effects on Stats
Over the past week or so I have talked about a simple and straight forward method for taking into account variations in zone starts. The method is to simply ignore the 10 seconds following an offensive or defensive face off. By adjusting for zone starts in this manner we can see a fairly significant impact on stats and today I’ll take a look at what gets impacted and how.
To do this I took a look at 3 year data using the 2008-09, 2009-10 and 2010-11 seasons. Using 5v5 data for players with at least 1000 minutes of ice time I identified the 25 players who had the highest percentage of their face offs in the offensive zone and the 25 players who had the highest percentage of their face offs in the defensive zone. I then compared their 5v5 zone start adjusted stats to their non-adjusted 5v5 stats. The statististics I looked at are on-ice goals for percentage, on-ice fenwick for percentage, shooting percentage, opposition shooting percentage, goals for per 20 minutes, goals against per 20 minutes, fenwick for per 20 minutes and fenwick against per 20 minutes. The changes are as follows:
|Top 25 OZPct||Top 25 DZPct|
What is interesting is that there are relatively small differences in GF% and FF% but differences in shooting percentages are very large (note that 15% change is from, for example, 10% to 11.5%, not the actual difference in shooting percentages). Goal and fenwick event rates are somewhere in the middle but while goal rates rise when we ignore the 10 seconds after an offensive/defensive zone faceoff, fenwick rates drop. This means that while a lot of shots are taken in the 10 seconds after the faceoff, very few of those shots end up as goals. As I mentioned yesterday, the league-wide shooting 5v5 percentage in the 10 seconds after the faceoff is around 3% while it is almost 9% the rest of the time.
Let’s look at some specific examples. Henrik Sedin gets a lot of offensive zone faceoffs and as a result 19.6% of his fenwick against events come within the 10 seconds after an offensive/defensive zone faceoff but only 8.0% of his on-ice goals do. In real numbers, Henrik Sedin was on the ice for 2634 fenwick for events and 523 occurred within 10 seconds of an offensive/defensive zone faceoff. He was also on the ice for 212 goals for while only 17 occurred within 10 seconds of an offensive/defensive zone faceoff.
Manny Malhotra is the opposite of Henrik Sedin and gets a lot of defensive zone faceoffs. As a result, 17.3% of all his fenwick events against occur within the 10 seconds after an offensive/defensive zone faceoff, but only 4% of his on-ice goals against do. In real numbers, Malhotra was on the ice for 1710 fenwick events against at 5v5 over the past 3 seasons, but 296 came within 10 seconds of an offensive/defensive zone face off. He was also on the ice for 75 goals against, but only 3 came within 10 seconds of an offensive/defensive zone faceoff.
What does this all mean? It means that if you are doing a corsi/fenwick/shot/shooting percentage based analysis accounting for zone starts is really important because it can have significant impacts on these stats (less so for ratios though). The impact on goals is much less significant but probably not something we would want to ignore depending on the analysis. May as well use the 10 second zone start adjusted data for all player analysis.