Goalies and the Playoffs Part 1: Why are Goalies Better in the Postseason?

Updated: January 11, 2018 at 1:41 am by Joel Short

A few years ago, I
started looking at the impact of goalie performance on success in the
playoffs. 

One of the first things I noticed was that the league
average Sv% tends to be significantly higher in the playoffs than in
the regular season.  Here are the averages going back to 83-84 (the
first year Sv% was recorded):

RS:P Graph 1

You can see a few
things right away:

  • Average Sv%
    has been rising over time. This is widely recognized, and the
    causes are pretty well understood.

  • The playoff
    average is more volatile (to be expected, since it’s a much
    smaller sample).

  • The playoff line seldom dips below the regular season.

  • The 80’s were nuts.

Over the last 32
seasons, the playoffs have averaged an 8-point higher Sv% (.008) than
the regular season. That’s a big gap – only 3 goalies in the
regular season this year out-performed the league average by 8 points
or more. 

So it begs the question… Why are goalies so much better in the playoffs? The most
obvious explanation is who’s playing (or rather, who’s not).
Teams tend not to play their backups in the playoffs, if they can
avoid it, and teams with poor goaltending are less likely to make the
playoffs at all. So let’s remove the goalies who didn’t play in
the
playoffs from each
year’s regular season
averages, and see if that
accounts for the difference.

RS:P Graph 2

As
expected, goalies who see playoff action do (on
average)
post better regular season
numbers than those who don’t.
Removing
non-playoff goalies
accounts for a good part of the gap (about 5 points on average), but
not all. The playoff Sv% is
still higher in most
years, at least until
recently.

But
if we want to know how much of the Sv% gap is due to who’s playing, we can do better than the
yellow line. A lot of backups do see playoff action, but don’t log
significant minutes. And we’d expect teams with better goalies to
go further in the playoffs, thus having a larger impact on the
playoff average. So lets take the regular season Sv% of each goalie
who plays in the playoffs, and weight it according to the number of
shots they face in that playoff year.

RS:P Graph 3

The
orange line – the average of goalies’ regular season Sv% weighted
by the number of playoff shots they face – represents what I’ll
call Expected Playoff Average
Sv% (EPA).
If playoff hockey is just like regular season hockey, with the only
difference being which goalies are playing (and how much), this
should look a bit like a trend line for the playoff average Sv% (the
only difference being normal variance due to the smaller sample of a
playoff year).

The
weighted average is only slightly above the unweighted average –
about 1.5 points – but it’s pretty consistently higher. This
fits my expectation that teams with better regular season goaltending
are somewhat more likely to advance in the playoffs, although I’m
not sure how I’d go about quantifying that advantage.

Again,
it’s expected that the playoff average is more volatile, because of
the smaller sample. I’m not sure that you could find causes for
individual peaks and valleys in the playoff line – we could chalk
it up to random variance, or just a handful of hot or cold goalies
wrecking the curve.

One
anomaly we can account for is the drop in all lines in 06 –
it’s clear that post-lockout rule changes (especially smaller
goalie equipment) depressed Sv% for a while. It’s less clear to me
what caused the crazy swings in the 80’s playoffs. 84, 86 and 87
have the largest gaps on record between regular season and playoff
Sv%. Then 88 had the largest negative gap. Was there a
goalie flu that spring? It’s bizarre.

95
is also unusual enough that I think there should be an explanation.
It’s the biggest anomaly since 88, and breaks up what would
otherwise be a 20-year run of playoff Sv% outperforming the regular
season (and an 18 year run of outperforming the Expected Playoff
Average).

Looking
at broader trends, I’ll propose that we can divide this Sv% graph
into 3 eras:

  1. The Wacky 80’s (~84-88): super-volatile playoff averages.

  2. The Playoff Bonus Era (~89-07): The playoff average Sv% out-performs the EPA Sv%. 95 is the only exception.

  3. The Playoff Deficit Era (~08-present): The playoff average generally
    under-performs the EPA Sv%. Only in 09 and 13 does it climb above.

Because
the playoff average is volatile, it’s hard to pinpoint the
start/end points of these eras. For example, it may be that whatever
instigated the third era began with the 05 lockout. But I do think
these trends are more than a coincidence. The fact that better
goalies play more in the playoffs than in the regular season somewhat
obscures the trends, but if we accept that the orange line represents
a reasonable expectation for the playoff average Sv%, there should be
some as-yet-unidentified factor(s) causing a) a couple decades of
better-than-expected playoff goaltending, and b) a more recent trend
toward worse-than-expected playoff goaltending.


To
sum up, here are a few unanswered questions:

  1. Why did average playoff Sv% tend to be higher than expected for so
    many years?

  2. Why is it now lower than expected more often than not?

  3. What was going on in the late 80s?

  4. Can we explain the very poor goaltending in the 88 and 95 playoffs?

I
have a couple theories for the first two questions, but I’d be
interested in readers’ thoughts as well.

Bookmark and Share