Fantasy Hockey Goalies and the PK Boost

Some hockey websites would have you believe that analyzing fantasy hockey goalies is guesswork. None other than the website opens their fantasy hockey series on goaltenders with the following note:

When it comes to ranking goaltenders, there’s no way to escape the guessing game.

If you subscribe to the above theory, then you shouldn’t be surprised when your guessing game leads to predictions such as Tuukka Rask being listed as the #1 fantasy hockey goalie heading into the 2010-2011 season (by the same author). That prediction was accompanied by the following quote:

I think it’s fair to say that Thomas is still a great goalie, especially mentally. But I don’t think Boston will have the luxury or reason to give him more than 20-25 games.

We all know how that season ended.

We don’t believe in guessing. We believe in developing methods that are predictive and repeatable. That’s not to say we can predict a goalie’s save percentage in the upcoming season (we can’t, you can’t, and there are reasons for this which we’ll describe below). But, with research and mathematics guiding the way, you can make an informed choice (not a guess) on which goalies are most likely to provide you with a solid chance of winning your fantasy league.

In two recent articles (Penalty Kill Save %, Projecting a Goalie’s Save %), we laid the groundwork for understanding how to break down a goalie’s overall save percentage. The key concepts are repeated here for emphasis:

  • A goalie’s overall save % is comprised of three parts: EVSV% (save % while at even-strength), PKSV% (save % while on the penalty kill), PPSV% (save % while on the power play).
  • The EVSV% is a measure of the goalie’s talent level.
  • The PKSV% fluctuates wildly from year to year and is non-repeatable.
  • Since the lockout, no goalie who has faced at least 400 shots against on the penalty kill (PKSA) has been able to maintain a PKSV% better than .892.
  • The PPSV%, whether very high or very low, results in negligible (.001) changes in a goalie’s overall save %.

To complement those two articles, we’d like to introduce the idea of the PK Boost. The PK Boost is a shift (upwards or downwards) in a goalie’s overall save percentage that is due entirely to fluctuations in the PKSV%. As noted above, the PKSV% is a non-repeatable statistic incorporated into a goalie’s overall save percentage. We know that the league average for PKSV% sits at .875. We also know that the year-to-year correlation of PKSV% data is close to zero. Thus, if a goalie has a particularly good (or bad) year for PKSV%, you can’t rely on those numbers when projecting forward for future seasons. So, how do you measure the impact of a particularly good (or bad) PKSV% season? And, more importantly, how do you correct for it? We do this by measuring the PK Boost.

The PK Boost can be measured by comparing a goalie’s PKSV% in a given season with the league average PKSV% (.875). For example, in the 2011-2012 season goalie Henrik Lundqvist’s PKSV% was .905. This number is well above the league average and well above many of Lundqvist’s PKSV% numbers from previous seasons. Using the math laid out in this post, we will compute Lundqvist’s overall SV% for last season as if he had performed at the league average while his team was on the penalty kill. We start with the following equation:

= (.8210)*(EVSV%) + (.1534)*(PKSV%) + (.0256)*(PPSV%)

We’ll plug in the league average for PKSV% and enter Lundqvist’s actual values for EVSV% and PPSV% to determine his adjusted overall save percentage. When we do this, we arrive at the following adjusted overall save percentage: .925. Now, to compute the PK Boost for Lundqvist, we simply take his actual overall SV% from last season (.930) and subtract off his adjusted overall save %. This reveals a PK Boost of 0.005 for Lundqvist. That is, 0.005 of Lundqvist’s SV% was due to non-repeatable statistical fluctuations of the PKSV%. Thus, you are on shaky ground if you’re expecting a SV% greater than .925 for Lundqvist in 2012-2013. Could it happen? It already has. Will it happen? Don’t bet your fantasy season on it.

Now that we’ve introduced the PK Boost and explained how to calculate it, we’d like to point out the recipients (or victims, depending on the direction) of the greatest PK Boosts from the 2011-2012 season. The table below reveals the goalie’s overall SV%, how much of that overall SV% was inflated (or deflated) by the PK Boost, and their adjusted overall SV% after correcting for the PK Boost. Note that we’ve left off goalies from this list who do not significantly factor into to your upcoming fantasy season.

PK Boost in 2011-2012
Goalie SV% PK Boost Adjusted SV%
Cory Schneider .937 +0.013 .924
Tuukka Rask .929 +0.007 .922
Johan Hedberg .918 +0.007 .911
Brian Elliott .940 +0.006 .934
Martin Brodeur .908 +0.006 .902
Ray Emery .900 +0.005 .895
Jonathan Quick .929 +0.005 .924
Carey Price .916 +0.005 .911
Marc-Andre Fleury .913 +0.005 .908
Henrik Lundqvist .930 +0.005 .925
Ilya Bryzgalov .909 -0.005 .914
Antti Niemi .915 -0.006 .921
Corey Crawford .903 -0.007 .910
James Reimer .900 -0.010 .910
Steve Mason .894 -0.012 .906

So, what does this all mean? For starters, when you look at our 2012-2013 Fantasy Hockey Goalie Rankings, you’ll now have a better understanding of why some goalies appear to have jumped or fallen in the rankings. More importantly, these numbers quantify exactly how much of a goalie’s performance last season was due entirely to PKSV% fluctuations (variance, or ‘luck’ if you like using that term loosely).

You can use these numbers many ways as a fantasy hockey manager. As a first approximation, you can get a qualitative feel for which goalies might experience a dropoff or rise next season (and you can even quantify the expected change). We don’t recommend using the PK Boost as a stand-alone tool. But, when used in conjunction with a goalie’s career EVSV%, you can make reasonable projections of a goalie’s expected statistics for the upcoming season. And that has to be better than playing the guessing game.

If you’re interested in winning your fantasy hockey league and (due to time constraints) want someone else to project the statistics for all NHL goalies based on this methodology, consider buying a Left Wing Lock Fantasy Hockey Draft Kit.

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