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Tag: PDO

Why Is VGK’s PDO Consistently Over 104, And Is It Sustainable?

(Photo Credit: SinBin.vegas Photographer Brandon Andreasen)

From the speed of play to the shape of the puck to the simple fact that the game is played on an unnaturally slippery surface, the nature of the sport of hockey lends itself to see outcomes determined by a fair amount of luck.

For years the stat nerds have tried to quantify the term “puck luck.” The idea is that once we identify what it looks like to be lucky, we can reasonably use the laws of variance to predict when a team will come back down to normal.

Baseball has been using these methods for decades. As the sport at the forefront of keeping and relying upon stats, it’s always been easy to see when a player is hitting .750 for a week, he’s probably going to regress in the near future.

That same idea is where our geeky friends came up with the term PDO. Like all good hockey stats, the name doesn’t make any sense. It literally doesn’t stand for anything as it was just a nickname of a blogger back in the early 2000’s. The stat is basically a measurement of puck luck as it adds shooting percentage and save percentage. The idea is that every shot results in a save or a goal, when you add them up for all teams the league average will always be 100%. So, a team or player with a PDO above 100 is lucky and expected to regress while a number under 100 is unlucky and expected to get better.

Why do I tell you all of this? Well, because the Golden Knights have been on an incredible run of fortunate PDO to start the season. They currently sit at 104.3 at 5-on-5 which is 2nd in the league behind the Vancouver Canucks (108.8). That means regression is coming. Right?

Hold on a second.

In the playoffs last season the Golden Knights won 16 of 22 games en route to winning the Stanley Cup and never faced an elimination game. They did it with an incredibly lucky PDO of 106.5.

Last year, after the All Star break, those same Golden Knights went 22-4-5 to win the Pacific Division and clinch the #1 seed in the Western Conference. They did it with an incredibly lucky PDO of 104.1.

Let’s recap. 104.3 this year. 106.5 in the playoffs. 104.1 in the latter half of the season last year. Some (most) would say this is unsustainably lucky and the team is in for a major regression in the near future. I’m a little more skeptical of that and have been beginning to wonder if maybe this is a trend more so than a blip.

Admittedly, I’m a believer in PDO for the most part. The current Vancouver Canucks, yeah, I think they’re going to regress big time. So typically, I’d see the numbers for Vegas and think the same. But, the numbers have stayed in the “unsustainably lucky” category for far too long to keep fitting this team into the same box as everyone else.

So, I set out on a mission to figure out why, or maybe how, the Golden Knights are doing this, and more importantly, if it’s sustainable.

After digging into the numbers in all sorts of different ways, the first part of the explanation as to how the Golden Knights have maintained a strong PDO is the location of the shots they take compared to the ones they allow.

Let’s start by looking at this year’s numbers. On the season, the Golden Knights have taken 269 shots on goal while allowing 306. Here’s where they’ve come from.

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PDO My God

Are these goals regulation size or what?!? (Photo Credit: SinBin.vegas Photographer Brandon Andreasen)

The stat PDO is hockey’s best indicator of a team’s relative “luck.” PDO is simply a calculation of offensive shot percentage plus team save percentage. In theory, those numbers should add up to 100%, anything above and the team is getting lucky, anything below and they’re unlucky.

The term luck can be heavily debated, and I tend to land more so on the side of saying luck is an excuse more than an explanation of what’s going wrong with a hockey team. That being said though, sometimes the numbers are so astounding that they cannot be ignored. That’s the case 12 games into the 2018-19 season for the Vegas Golden Knights.

Their shooting percentage is 6.34%, last in the league, and their save percentage is 88.78%, 24th in the league. Add them up and you get a PDO of 0.951, tied for 31st in the NHL. It gets even worse if you drop special teams and look only at even strength. Then the Golden Knights PDO is 0.942, far and away the worst in the league.

So what does this mean? Well, for starters, it means based on the number of shots taken and number of shots saved, the Golden Knights are between 14 and 20 goals short of a 1.00 (average) PDO. That’s well over one extra goal per game.

For you math nerds, the Golden Knights PDO is 2.27 standard deviations from the league average after 12 games. For those who have no clue what the heck that means, historically, teams one standard deviation away from the average are considered unlucky. Teams two standard deviations from the norm are considered extremely unlucky. The Golden Knights are 2.27 away, so they are pushing some sort of voodoo magic level of bad luck.

Of course, a 7-0 game here or there could completely swing that number back without seeing a massive impact in the standings, but if it’s a slow burn back to the 1.00 number, or anything close, we’re literally talking about a goal a game difference.

There are many reasons to explain it and there’s no question a portion of the numbers rest on the shoulders of poor play by the Golden Knights. However, there’s a difference between a couple of missed opportunities and a couple of breakdowns and a 0.951 PDO.

Since 2007-08, no team has finished with a PDO of less than 0.966. If the Golden Knights were sitting at that number right now, they’d have about five more goals. The worst shooting percentage over that span is 6.9%. Vegas’ is currently 6.34%. If they had that extra roughly 0.5% back, they’d have another three goals. And these are comparisons against the worst teams in 10 years!

However you want to slice it, the fact of the matter is the Golden Knights will not finish the season with a PDO anywhere close to what they currently have now. When it comes to shooting percentage and save percentage, things will change and in a big way. That’s not a prediction, that’s a statistical fact. (Well, as long as you don’t believe the 2018-19 Golden Knights are the one in a 34 billion to 1 situation.)

**Stick tap to our good friend Marissa (@Taxpro4gamblers) for helping with the in-depth mathematical analysis used in this article.**

Advanced Stats For VGK Dummies: PDO

We’ve already taught you about Corsi, Zone Starts, and First Assist, now it’s time for the fourth installment of the ever popular segment. Today we’re taking on a slightly more complicated one… PDO. The NHL refers to this stat as SPSV%.

Tim Barnes ran the now defunct website Irreverent Oilers Fans. While doing so he used the pseudonym Vic Ferrari. Brian King was another writer on the site and used the nickname PDO. Barnes began delving into stats and came up with the terms Corsi and Fenwick, and eventually with the help of King came up a stat they named after King, calling it PDO. Or something like that, the story gets twisted a lot.

Yeah, but who gives a damn about the name, just tell me what the hell it is. Fine, calm the F down. But first, remember that PDO and SPSV% are the same thing. For the remainder of this article, we are calling it PDO, cause it’s cooler and the NHL is lame for changing it.

PDO is the sum of shooting percentage and save percentage while a player is on the ice. Shooting percentage is number of goals scored divided by total number of shots of all players on that players team while on the ice (oiSH%). Save percentage is number of saved shots divided by total number of shots by the opponent while a player is on the ice (oiSV%).

(Similar to Corsi, it doesn’t matter if an individual player actually takes a shot, all that matters is that he’s on the ice when a shot is taken or a save is made.)

Example time! Erik Haula is on the ice for a total of 10 minutes during a game. During those 10 minutes, the Golden Knights have 20 shots and 1 goal. In those same 10 minutes the Kings have 10 shots and also have 1 goal. Therefore, nine saves were made by the Golden Knights while Haula was on the ice.

On Ice Shooting Percentage (oiSH%) – 1/20 = 5%
On Ice Save Percentage (oiSV%) – 9/10 – 90%
PDO – 5% + 90% = 95

PDO is usually measured against the number 100 because a shot is either scored or saved. Think of it like flipping a coin. It’s either heads or tails, so over the course of all flips, the percentage of heads plus tails will be 100%. Under the same mathematic principle, the average of all shots made plus all shots saved will be 100%.

The working theory in hockey is about 8% of shots are made meaning 92% are saved. So, over time, player’s PDO numbers should regress toward 100 (8+92).  Of course, that’s ridiculous because some players are better than others and luck is heavily involved in hockey, but a player’s PDO can often be an indicator of the future of a player’s season or career.

Let’s look at some Golden Knights PDO numbers. Forwards first…

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