Why are goalie save percentages rising?

Eric T.
October 09 2012 09:30AM

League average save percentage is on the rise

Save percentages have been increasing sharply in recent years. Some of this is because there have been fewer penalties called, but even just at even strength we see a clear increase in save percentage.

How do we explain this?

Better defense?

One possibility is that teams are committing more on defense and pushing shots to slightly less dangerous locations. However, we can calculate average shot distances using Behind the Net's data, and while the trend is unclear, it certainly does not suggest that shots have been pushed farther out in recent years:

League average shot distances have not gotten longer

Of course, distance isn't the only factor that determines how dangerous a shot is. Angle can also be a key factor. If we saw more bad angle shots from a similar distance, we would expect to see an increase in the x-coordinate (distance from the center of the goal towards the boards), as shots go from being directly in front of the goal out towards the sides. However, that is not what has been observed:

Shot angle appears to be largely unchanged

The pattern in the last three years is a bit bizarre, with certain distances (1, 3, 5, 7, 10) much more likely than others (2, 4, 6, 9, 11). It is also interesting that this pattern was not observed in 2008-09; I wonder whether the NHL's official scorers went through some kind of standardization training after that season that led them to converge on this specific recording pattern.

But I'm getting sidetracked; the point is that the x-coordinate has scarcely changed over the years, and if the distance hasn't changed, then that tells us that the angle hasn't changed either. In other words, save percentages aren't going up because the shots are coming from less dangerous spots.

That would seem to suggest that either shooting skill is going down or goaltending skill is going up. I suppose either is possible, but with athlete strength and speed (and composite stick technology) continually improving, it seems unlikely that shooters are getting worse. So I'm going to proceed on the assumption that goaltending is actually getting better, and then the question is why -- are the individual goalies getting better (via improved training, refinements of technique, video analysis of shooters, etc) or is the pool of goaltenders getting deeper?

Can you teach an old goalie new tricks?

To answer this, I looked at the 24 goalies who have played at least 10 games every year since the last lockout to see whether their save percentages rose in parallel with the league average or whether the effect came from new goalies coming into the league who were bringing the average up. I also focused in on the 12 who were starting goalies over this period (never fewer than 25 games played in this sample, averaged over 40), in case the lesser goalies added more noise than value.

Individual goalies' save percentage does not mirror the league average

It doesn't appear that the rise in the league average came from individual goalies getting better; our sample that played for the whole period ended up almost exactly back where they started (.91949 in 2006, .91944 in 2012), and the trend is very similar for the reduced data set.

There is a potential confounding factor of age here, however. If a goalie was benefiting over time from adopting improving approaches, that might lead to steeper improvements as he entered his prime (his normal development plus new techniques) and less decline as he exited his prime (normal aging offset by improved techniques). So if the goalies in our sample were mostly in the back half of their careers, a real effect might be obscured -- seeing a plateau rather than a decline from those older goalies might actually be a sign of improving methods.

Luckily, the guys we are looking at happen to cover a reasonable spread of ages. There are some like Dwayne Roloson and Martin Brodeur who were on the decline, but there are also some like Cam Ward and Marc-Andre Fleury who are just now hitting their prime. As a result, while the impact of age and development might not be perfectly averaged out, it should at least be muted. The baseline expectation for this group of mixed ages should be something close to flat.

And indeed their aggregate performance was flat, so it's unlikely that the individual goalies were getting better -- collectively, this group ended up right where they started. So if the improvement in league-wide save percentage didn't come from shooters getting pushed to the outside, and if Miikka Kiprusoff and Tomas Vokoun and Roberto Luongo and Ryan Miller and Fleury and Kari Lehtonen and company weren't getting better, then what changed is that the talent pool got deeper. Save percentages went up because the rest of the league got better.

The goalies in this sample combined for 7592 starts over this span, just over 44% of the league's playing time. While their save percentage was exactly level over these years, the rest of the league was improving dramatically -- from an even-strength save percentage of .911 in 2005-06 to .922 in 2011-12.

Out with the bad, in with the good

In 2005-06, Martin Gerber, Alex Auld, Marc Denis, David Aebischer, Robert Esche, Antero Niittymaki, Mathieu Garon, and John Grahame were all starting goalies. Add in a couple of big-name goalies who were well past their expiration date like Ed Belfour and Curtis Joseph and it's fair to say that at least 1/3 of the league had a genuinely bad starting goalie.

In 2011-12, you might put Steve Mason, Garon and Jonas Gustavsson in that category. But the rest of that list has been replaced with the likes of Carey Price, Jaroslav Halak, Jonathan Quick, Jimmy Howard, Jonas Hiller, and Pekka Rinne.

The pool has grown much deeper; facing the same quality shots, there are a lot more goalies capable of holding their own than there were a few years ago. Having a top goaltender used to be a real advantage, but now it is expected -- instead, not having a strong goalie is a disadvantage.

The question for general managers is whether this should be expected to continue. If so, then locking up a goalie long-term means watching the rest of the field continue to improve while your goalie stays the same. The continuing improvement in the goalie pool would make it analogous to the electronics market -- your $1500 television might be really cool for a while, but in a few years you'll be jealous of your buddy who gets a nicer one for $800.

It may still make sense for a contender that needs a quality goalie to take advantage of a window of opportunity, but a team that is still building towards its peak needs to consider this trend before signing a goalie to a long-term deal.

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Eric T. writes for NHL Numbers and Broad Street Hockey. His work generally focuses on analytical investigations and covers all phases of the game. You can find him on Twitter as @BSH_EricT.