Power Play - Shots vs. "Shot Quality"

by Derek Zona on Dec 20, 2011 4:30 PM MST in Statistical Analysis

This is one of the stat side of things that I either don’t understand or don’t agree with. I can see the relationship between shots generated and powerplay goals. But obviously the quality of the shot plays a role in how many goals actually go in. Is the arguement that over time high quality chances are unsustainable?
--Peacecountry, in the comments .

A quick check of the data from the last four years via the venerable and terrifying Gabriel Desjardins shows the relationship between shots per sixty minutes of 5v4 time on ice and power play success (power play conversion percentage) is extremely strong, with an r^2 = .400 So, given our sample size, 5v4 shots per 60 predicts 40% of power play success.

But the Oilers are 24th in the league in shots per 60, which is a mountain to climb if they want to have a top 10 power play. Put simply, four teams in the last four years have had a top ten power play by percentage and finished in the bottom ten of the league in shots for per 60 with the man advantage. The teams to pull off this feat were Philadelphia and St. Louis in 2008-09, Minnesota in 2009-10 and St. Louis in 2010-11.

St. Louis ranked 29th in SF/60 in 2007-08, 24th in 2008-09, 15th in 2009-10 and 23rd in 2010-11. Mr. Desjardins has shown that a team's power play shooting percentage in half of its games has almost no predictive ability for guessing how it will do in the other half, so we should attribute a high shooting percentage to luck rather than a scheme that produces high quality shots.

If the argument for shot quality on the power play rests on St. Louis, we must assume they forgot how to take quality shots in two out of these four seasons.

Another way of looking at this: over the last four years, there have been 120 individual seasons. Of the top half of all power plays during that time (60 of 120) only eight of those teams finished in the bottom ten in shots for per 60 with the man advantage. While there is gray area in there (some top 10 teams obviously finished in the middle 10 in shots), the jump from the bottom in shots to the top in conversion is a difficult one.

It's possible to have a top ten power play with bottom ten shots generated, but it's not desirable, nor is it necessarily a product of shot quality, but more likely a product of variance. So, yes, Peacecountry, the Oilers might finish in the top 10, but it's going to be based on luck, not shot-quality.

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Backed Into the Corner

…unfortunately for the Oilers they waited too long before thinking about adding help on the blue line. The players that could be traded for a blueliner (MPS, Omark, Gagner et al) aren’t playing well enough to command anyone of stature; furthermore anyone worth their snuff on the blueline is going to command too high a price.

That being said, if the D-men would pass the puck with authority, even off the backboards, it would cut down on the turnovers and scoring chances against; and, the atrocious line changes need work now as the too many men penalties and just blockheaded changes are costing goals and games.

Although the overview of statistics helps analyze what’s gone wrong, the way out of the mess is to play smarter…this could be coaching woes, maybe Renney just isn’t the guy, and poor line changes bear that out.

Irrespective of the stats, this team is better to watch, when it plays, than last years version and although fading quickly, the playoffs are still a possibility if management can instill a dose of confidence. I look at Jason Garrison and Nick Leddy and wonder why the Oilers haven’t been able to bring around some of the defensive prospects more quickly. Mobile puck moving defense is the key to success and until that happens the team is an also ran.

I worry that the fine young talent will get a loser mentality and a Tampa Bay Lightning type of team is going emerge. IMO

by Otiepitotie on Dec 20, 2011 4:56 PM MST reply actions

Just spitballin'

The average shot taken on a power play probably is “better quality” than the average shot taken at evens. Due to the dynamics of a power play, NHL teams probably don’t take many shots on the power play that aren’t dangerous. So, in other words, the higher shot count is actually reflective of a team using good board work / puck movement / hustle / %110 / poise to make the play (in the same way that corsi / fenwick are).

by samspade on Dec 20, 2011 6:34 PM MST reply actions

Sorry if that seems like I’m saying “OMG the sky is blue!!!”

by samspade on Dec 20, 2011 6:35 PM MST up reply actions

And yes, there is a higher likelihood that a shot taken on the powerplay will go in than a shot taken at 5v5.

Ryan Popilchak

Matchsticks & Gasoline, Artic Ice Hockey, &Hockey Prospectus. My twitter handle is @sprtopinionated

by SO_RyanP on Dec 21, 2011 6:55 AM MST up reply actions

Or simply put, the NHL is a very competitive league now. Any system developed will be countered quickly. Nearly all of the players are fit, and there is a lot of money on the line for them. Only player quality can change the balance. Therefore, the more times you get a shot on the net, the more times you are likely to score, so the more goals over a season. And the better players you have, the more shots will find twine. Because of the level of competition, it is very hard to maintain any advantage in shot quality or team system. What matters is the quality of players and their level of commitment.

by FastOil on Dec 20, 2011 7:12 PM MST reply actions

The shot quality argument (that there is no such thing) is a case of drawing an inference on the basis of noise in the data.

So while it is indeed true that shooting percentage is not, in a statistical sense, a repeatable skill, the inference that then there is no meaningful difference in shot quality does not necessarily hold.

However, the converse is also true. Which is to say that a high shooting percentage is not, in itself, evidence of a skill in getting quality shots.

In both cases there is too much noise in the data to make any direct conclusion. The only reasonable conclusion to make on the basis of experience/knowledge of the sport combined with the available data is:

1) differences in shot quality are real (opportunities created)
2) differences in finishing ability are real
3) however there is not data sufficient to conclude either 1) or 2) on the basis of data alone.
4) Hence there is no way to differentiate between skill and luck on the basis of results alone

by Captain Obvious II on Dec 21, 2011 11:53 AM MST reply actions

So shot quality exists, the sample size isn’t large enough? How much data do you need?

Editor of The Copper & Blue, and leader of The Cult Of Hartikainen.

by Derek Zona on Dec 21, 2011 8:07 PM MST up reply actions

I really appreciate the time it took you to answer my post. At times it’s hard to believe in the statistics when they are presented. I’m trying but I need a nudge every once in a while

by Peacecountry on Dec 21, 2011 7:09 PM MST via mobile reply actions

There’s a larger chance that shot quality exists at an individual level on the power play compared to even strength. But in the overall picture, of what we know, it’s persistence of shots that pays off.

Editor of The Copper & Blue, and leader of The Cult Of Hartikainen.

by Derek Zona on Dec 21, 2011 8:06 PM MST up reply actions

Speaking of the individual, what are the chances the Oilers have happened upon an outlier in RNH, in terms of PP performance?

by hockeysymposium on Dec 21, 2011 8:34 PM MST up reply actions

It’s possible, but you probably wouldn’t want to hitch your wagon to that horse after only 30 games.

Editor of The Copper & Blue, and leader of The Cult Of Hartikainen.

by Derek Zona on Dec 21, 2011 9:03 PM MST up reply actions

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