On the weekend I posted an article looking at the relationship between Corsi and Shooting percentage and suggested that good Corsi teams are often poor Shooting Percentage teams and that there is generally a negative correlation between Corsi and Shooting percentage. This relationship seems to hold for most teams except for the elite teams or the truly bad teams. Yesterday over at MapleLeafsHotStove.com I looked at this relationship just prior to, during, and just after the Randy Carlyle coaching era and it seemed to hold true (to some extent) for the Leafs during that time period.
These kind of relationships sometimes brings on a negative reaction among those familiar with Hockey Analytics and in particular those that believe strongly in possession and Corsi. I sometimes wonder why this is because we see this relationship occurring all the time with score effects and score effects is a well known and accepted concept in hockey analytics. Let’s recall what score effects are:
- When a team is leading they will generally give up more shots and take fewer (resulting in a depressed Corsi) but generally the shots given up are of lower quality resulting in higher save percentage and the shots taken are of higher quality resulting in a higher shooting percentage.
So, due to some difference in playing style, when a team is leading they will see a drop in their Corsi and a boost in their shooting percentage. This is the exact same thing as the negative correlation I am observing in these articles. Why people find it hard to accept here but accept score effects is beyond me but some people have trouble with this. In any event, I want to take a look at how the relationship between Corsi (CF%) and shooting percentage has changed over the course of the season for the four teams that have made a coaching change thus far – Senators, Oilers, Devils and Leafs. Let’s look at these teams in reverse order and start with the Leafs first because I have already discussed them in the MapleLeafsHotStove.com article and I’ll leave the Senators to last since they have the most interesting results. So, with that said, here is the 5v5 CF% vs Sh% chart for the Maple Leafs this season.
The black line indicates the time of the coaching change and what you see are the rolling averages over a 500 corsi event (for + against) sample. The correlation between these two is -0.20 so we do see a negative correlation. What we also see is that the Leafs CF% was actually rising under Carlyle prior to him being fired and the shooting percentage had already started falling off as well.
How about the New Jersey Devils?
The correlation between CF% and Sh% for the Devils is -0.38, or a fair bit stronger than for the Leafs. The Devils have been on a run of much improved shooting percentage recently but that has corresponded with the lowest CF% levels of the season. While Sh% seemed to be on the rise prior to the coaching change it did jump up a bit more after the coaching change though has dropped back the last little bit. Overall the highest shooting percentages on the season have occurred after the coaching change which is also when the Devils have had their worst CF%. Surprisingly, the Devils might be one of the worst possession teams in the league right now.
And the Oilers?
The negative correlation is quite strong here as the correlation coefficient is -0.795. Early in the season the Oilers had a low CF% and a higher shooting percentage which then reversed into a higher CF% and a lower shooting percentage before them both converged in the middle just prior to the coaching change. After the coaching change the Oilers CF% dropped to season lows while shooting percentage jumped back to early season highs (though it has fallen off in recent games).
For the Leafs, Devils and Oilers it is difficult to say that their coaching changes have had a major impact thus far (maybe for the Leafs but it is too early to tell) as it seems for all teams their post coaching change trends appear to have actually started just prior to the coaching change. Everything is different for the Senators.
Unlike the three other teams, the coaching change in Ottawa appears to have a significant positive impact as both their CF% and their shooting percentage has increased dramatically from where they were just prior to the coaching change. When you see stuff like this you really wonder if this is in fact one of those instances where the coach (in this case Paul MacLean) really did lose confidence of his players. The coaching change really did seem to have a positive impact on both CF% and shooting percentage. This surge in both CF% and shooting percentage means the two statistics are positively correlated over the course of the season with a correlation coefficient of 0.30.
In the future I’ll maybe take a look at a few other coaching changes from past seasons (i.e. Pittsburgh hiring Bylsma, Anaheim hiring Boudreau) to see how they looked and I might also take a look at save percentages as well. So far though all evidence points to the existence of a negative correlation between CF% and Sh% though there are also some exceptions to that rule like the Ottawa Senators after their coaching change.