Most people will agree, at least at some level, that possession of the puck plays a major part in game outcomes. How long you can control the puck may be a lot more important than many people realize. The exact value of possession is hard to quantify (not due to lack of ability, but because of lack of data). Many commentators talk about the importance of battles along the boards, face-offs and give-aways and take-aways. So how important is it really?
First off using the limited data available, how do you research possession? That isn’t easy, but certain events say something about possession, for example you must have possession to take a shot, if you win a face-off you have possession after the face-off. If you hit a player you shouldn’t have the puck (otherwise it should be interference). A blocked shot indicates you didn’t have possession. The NHL provides a couple obvious possession pieces of information in give-aways and take-aways (they say something both before the event and after). Using this data one can be reasonably sure about certain amount of time of the game (I believe it worked out to 50-70%). The rest is still up in the air, but in terms of averages it works out quite well.
Now when I originally did the study I found there was little or even negative correlation between possession and winning individual games (which was a surprise). However, when I averaged the data over the season I got some interesting data. I have two graphs.
The first graph (winning percentage vs. predicted wins) shows the standard Pythagorean prediction of winning using goals for and against. [Has a R2 of 86%]. The second one (winning percent vs. possession) compares the teams winning percent (or points) over the season to their percentage of possession [Has a R2 of 92%]. Now just considering their R2, possession is a better predictor than the Pythagorean prediction. Now this is a small data set, and I hope to test it on more data, but in general being able to control the puck when you need to will result in more wins.
Why might this be? If you think about hockey if you have the puck the other team can’t score and if you don’t have the puck you can’t score. If you’re winning by one goal in the third period and you control the puck you are more likely to win, and if you are down and control the puck you’re more likely to get that tying goal and as such win (or OTL). So puck possession shows the difference between good and bad teams. The question that should be answered next is how then can a bad team possession wise (8th seed) do so well in the playoffs vs. better possession teams. I’ll save that for another day.