Monday, May 04, 2009

Possession Is Everything

I think that Mike Babcock is right, possession is everything. Damn close to it at even strength, anyways. I also agree with his thinking that being a "puck possession(TM)" team has little to do with coaching style, and everything to do with how good your players are.

Scott sent me Dennis' scoring chances for 77 Oiler games this year, cleanly formatted in game by game fashion. So it was fairly easy to drop the scoring chances by game and player into an array, along with the on-ice goals and on-ice shots directed at net (corsi). All the information used in this post is for even strength ice time only.

From there it's simple enough to grab the top 20 skaters by ice time (Stortini being the cutoff point), randomly select 40 games from the season, and see how well EV scoring chances correlates with goals and corsi in those games.

Here I used percentage of the total, it saves buggering about with ice time and seems more relevant in any case. So if, in those 40 games you were on the ice for 20 goals-for and 30 goals against ... that would be a goals rating of 40%. i.e. 40% of the goals that happened were for your team. Same for scoring chances and corsi.

I wrote a script to randomly select 40 games from the season and calculate the correlation. And then to do the same 1000 more times. And as shown in the chart above, after 40 random Oiler games this past season; the correlation of scoring chances to corsi averages .84, and the correlation to goals averages .59. Both strong relationships.

And then I repeated the excercise for 10 game samples, 20, 30, 50 etc.

The idea is that the more games you're looking at, the more luck washes out. And you can see that over a small batch of games the player's scoring chance rates mesh reasonably well with results (goals) for these 20 Oiler players as a group. But as the sample of games grows larger, near the 77 total, the relationship becomes overwhelming and obvious. And if the season were 40 games longer there is every reason to think that the correlation would grow even stronger, even though there isn't much room to grow at that point.

And corsi, our best guess at territorial advantage using readily available stats, it becomes remarkably similar to scoring chances given enough games of data.

In this season, the on-ice shooting% was spread fairly evenly across the board, so the relationship of scoring chances to goals is stronger than it will probably be most years.

Bottom Line: Players that drive possession at EV drive results at EV. Maybe not the next game the Oilers play, or the next dozen, but eventually. It's unstoppable, ability trumps luck eventually, you just have to be patient.

5 Comments:

Blogger Vic Ferrari said...

Just to add:

Corsi begets scoring chances, scoring chances beget goals, and even over the course of a full season the hockey gods have a huge say in a player's scoring (and outscoring) results, and a big say in the same results for the team.

And while corsi may not be a perfect measure of territorial advantage, it's still terrific, moreso than any of us thought, I'm sure.

You can make a good estimate of a player's scoring chance numbers by using his corsi. And I suspect that the difference is largely luck, scoring chances drifts toward the highly repeatable corsi.

And, as always, without context (quality of opponents, linemates, own zone shift starts, etc.) all stats have much less value at the player level.

5/04/2009 8:04 pm  
Blogger Scott said...

This is great stuff Vic. I haven't gone on to read parts three and four and more yet but It's exciting to see what might come of the data.

The big takeaway for me is that (as is obvious even without the numbers) a lot of players get too much flack for not producing in the playoffs. Guys like Thornton, the Sedins and formerly Datsyuk and Hossa. The playoffs are such a small sample even for a guy that's played "a lot" of games relative to his peers. Very few guys make it to 100 games without doing well and if you've been bad over 20 games or so you've already earned your label (at least from fans and media).

5/05/2009 3:00 pm  
Blogger Vic Ferrari said...

Yeah, I think that the first statsy hockey thing I read on the web, at least a decade ago, was on puckerings.com. And the author showed that previous playoff scoring was a poor predictor of future playoff scoring.

Regular season scoring, for that year or more, was much better.

I doubt that the shots numbers for these guys change much to the playoffs (their own or the on-ice ones) but the percentages probably took a kicking.

In the case of Thornton/arleau this season though, the matchup against Getzlaf/Perry/Ryan was unkind by eye, and surely by the numbers. Zetterberg's line played against them in G2 (and probably in G1, never saw it) of this series and Getzlaf's line looked to have the better of them by a wide margin. And that's with Lidstrom usually on the ice as well. A terrific line right now. And keeping Ryan in Junior and then the minors ... doesn't see to have hurt his development at all. I wish the Oilers had done the same with Cogliano and Gagner.

5/05/2009 3:40 pm  
Blogger Vic Ferrari said...

For trivia darts fans:

'Corsi' is your ability to answer sports trivia questions against me, as recorded from previous games by the bartender. And if you win then you get a 'scoring chance'. Down here at the pub 'scoring chance' means a chance to throw a dart at the board. Hit the bull or double bull and you get a dollar.

Of course if I win the trivia contest I get to throw a dart.

A word to the wise: If you are ever a captain of a trivia darts team, never put up a crappy trivia player against Lain, even if they are great dart throwers ... that never ends well. I like to play Dennis against Lain (he can answer trivia AND throw darts), and then set myself (I can answer trivia, but can't throw darts worth a damn) up against the Joffers* on the other team.

Of course it's different when we travel to play.

Sorry to get off topic.

* Joffers: Guys who are crap at trivia but the bomb at darts.

5/06/2009 3:51 pm  
Blogger Jim Philips said...

It si quite impressive that it has a impact like that. I didn't got until I tried the price per head free demo

5/30/2013 10:06 pm  

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