The Pittsburgh Penguins are in the midst of another Stanley Cup playoff run. With a 3-1 lead over the Ottawa Senators, they are a mere 1 game away from their 3rd Eastern Conference Final in 6 years. But it looks like they will do so without starting goalie Marc-Andre Fleury.

After a string of disappointing playoff games, Fleury has been benched and netminder Tomas Vokoun has been guarding the goal. And Vokoun is playing so well that it doesn’t look like Fleury will see the ice anytime soon.

So what does this have to do with statistics? Well, Fleury’s statistics tell the story of why he is on the bench. It all started last year, so let’s compare his regular-season save percentage to his playoff save percentage for the 2011-12 season.

• Regular Season: 0.913
• Playoffs: 0.834
• Difference 0.079

That’s a difference of almost 8% between regular-season and playoff games! To put this in perspective, let's say goalies typically face 30 shots a game. If they save 91.3%, they’ll allow 2 or 3 goals. If they save only 83.4%, they’ll allow 5 goals!

The difference between Fleury's regular season and playoffs wasn’t quite as bad this year (he was 2.5% worse in the playoffs), but combined with last year that was enough to put him on the bench. So what I want to know is, was Fleury’s playoff blunder the worst playoff performance ever? Is there any goalie who ever had a bigger differential between their regular-season and playoff save percentages?

# The Goalie Data

I collected data on every NHL goalie since 1982 (the dataset I used actually went back to the 1940s, but didn’t include "shots against" before 1982, so I couldn’t calculate save percentage). For each year, I calculated every goalie's difference in save percentage between the regular season and playoffs. The goalie had to have faced at least 50 shots in the playoffs in order to be included. I did that to exclude small samples, like Glenn Resch, the Flyers goalie who allowed a total of 1 goal on 1 shot in the 1986 playoffs.

# The Relationship between Regular- Season and Playoff Save Percentage

In total, the data set had 542 different observations. I’ll start by using Minitab Statistical Software to perform a regression analysis between regular-season and playoff save percentage.

We see that there is a weak positive relationship between regular season save percentage and playoff save percentage (the R-Squared value is only 16.5%). But the positive relationship makes sense, as the better a goaltender is in the regular season, the better he should be in the playoffs.

In the graph above I’ve marked Fleury with an upside-down black triangle. I drew a line at regular-season save percentage = .900 because of all the goalies to have a save percentage of at least .900 in the regular season, none have had a worse playoff performance than Fleury last year. The model would have expected him to have a save percentage around .906, instead of the .834 he actually had. Nobody in the “Above .900” group has ever had a playoff save percentage that low.

But was his difference the worst of all time? No. We can clearly see a goalie in the bottom left that had a regular season save percentage around .86, and a playoff save percentage around .75. That's a difference of 11%, which is worse than the difference of 7.9% Fleury had. But other than that, it’s hard to tell how many other goalies have performed worse from this graph. We’re going to need another plot in order to determine the worst playoff performance ever.

# The Worst Playoff Performance Ever

Luckily, Minitab has a plot that will help us out. I’ll make an individual value plot of each goalie's difference between regular season and playoff save percentage. The individual value plot will show us every single observation in the data set, so we’ll easily be able to compare who is the lowest.

We see that most of the points are clustered around 0. This makes sense, since in the long run you would expect goalies to play about the same between the regular season and the playoffs. But let’s get to the outliers! Again, I’ve marked Fleury’s performance from 2011-12 with the black triangle. But here it’s much easier to see who has performed worse. However, there are only 7 other goalies who have a worse differential!

So, who is the data point all alone in the bottom left?

That would be former Boston Bruins goalie Rejean Lemelin. During the 1989-1990 season he posted a save percentage of .892 in 43 regular-season games. But in the playoffs his save percentage dropped to .772, which is a difference of 12%! And don’t think that was because Lemelin was a terrible goalie...in the regular season of that same year, he teamed up with his goaltending partner Andy Moog to win the NHL’s William M. Jennings Trophy (for fewest team goals allowed).

When the playoffs began in 1990, it was Lemelin who started in goal for the Bruins. But when he struggled in the first few games, Moog came in and saved the day. In the opening round, Boston was losing their series 2-1 and found themselves down 5–2 entering the third period of game 4. Moog replaced Lemelin in goal and posted a shutout for the remainder of the game. The Bruins then rallied by scoring four goals in the third period to win the game. Moog would remain in goal the rest of the playoffs, leading the Bruins to the Stanley Cup Finals (where they would lose to the Edmonton Oilers).

How cool is that!?!?! It’s not every day that you do a statistical analysis and find that the answer to your question has such a neat story. Well, it probably wasn’t neat for Lemelin at the time...but at least he’ll always have that William M. Jennings Trophy!

# Do the 2013 Penguins = the 1990 Boston Bruins?

We’ve shown that it’s quite rare for a goalie as good as Fleury to have as bad of a playoff performance has he had in the 2012 playoffs. And while his performance this year wasn’t as bad (it’d be a much different story had he not shut out the Islanders in Game 1), it was enough for the Penguins to turn to Vokoun. But the Boston Bruins are a prime example of a team making a long run in the playoffs with their backup goalie!

So can the Penguins follow suit and do the same thing? If they finish off Ottawa, there will only be one team standing between them and the Finals. And of course, it’ll most likely be the Boston Bruins. Oh, the irony! But should we have expected anything different? Absolutely not. Why? Because It’s The Cup!

Photograph by wstera2.  Licensed under Creative Commons BY-NC-SA 2.0.