Thursday, May 29, 2008

Shot Prevention

We have had a very interesting discussion lately in the comments about whether goalies can reduce shots against. It has been demonstrated, and I agree with the math presented, that if goalies are able to reduce shots against by 2 per game that would be roughly the equivalent of an extra .005 in save percentage. However, it still has not been demonstrated that an effect that large is actually observed among NHL goalies.

I'm going to focus on Martin Brodeur, again, but as he is one of the gold standards of puckhandling as well as rebound control it makes sense for us to do so. I am going to look at the shots against statistics of his backup goalies to see what kind of information that gives us about New Jersey shot prevention.

Here are all of Martin Brodeur's backups that played at least 150 minutes for New Jersey and at least 150 minutes somewhere else in the league between 1993 and 2008, listed with their shots against averages in New Jersey and for the other teams they have played for (1993-94 to date, to coincide with Martin Brodeur's career):

Scott Clemmensen: 26.6 in NJ, 24.2 elsewhere
Corey Schwab: NJ: 21.7 in NJ, 29.0 elsewhere
Mike Dunham: 26.5 in NJ, 29.7 elsewhere
Chris Terreri: 27.0 in NJ, 28.8 elsewhere
John Vanbiesbrouck: 23.3 in NJ, 27.6 elsewhere
Kevin Weekes: 28.0 in NJ, 29.5 elsewhere

Most of these are very small sample sizes, so we need to look at the aggregates. Overall, Brodeur's backups played 10,748 minutes and faced an average of 26.1 shots per game, 0.7 more than Martin Brodeur himself. This average is skewed by Chris Terreri's season in 1993-94 when he split time with Martin Brodeur. Since Brodeur would go on to play so many games per year from 1995 to present, Terreri's minutes from 1993-94 make up nearly a quarter of the total backup sample, and the league was still relatively high-scoring (and high-shooting) that season compared to later in the decade. If you take a year-by-year average of shots against by backups, the result is 25.4 shots per game, exactly the same as Brodeur's career mark. For the group, the average shots per game outside of New Jersey was 28.9, nearly a 3 shot per game difference.

Let's look at some of the other stats. Every single backup goalie listed above had a better winning percentage for the Devils than for the other teams they played for. Except for Kevin Weekes, all of them also had a better save percentage and GAA in New Jersey than elsewhere.

NJ backups: 73-64-19, 2.52, .904, 26.1
NJ backups elsewhere: 461-600-170, 2.77, .904, 28.9

The save percentage numbers are interesting - exactly the same in New Jersey as everywhere else. Is there an explanation for this? Does this invalidate the shot quality measurements that claim New Jersey had the league's best defence? No, it does not, because this is a simple sum total of all the backups' stats, and again the stats are skewed. Chris Terreri makes up about half of the New Jersey minutes but less than 10% of the non-New Jersey minutes, while John Vanbiesbrouck only had 540 minutes in New Jersey compared to over 27,000 minutes on other teams.

To deal with this issue, I weighted the goalie stats based on New Jersey minutes played, and here are the results:

.419 win %, 3.08 GAA, .891 save %, 28.4 shots/gm

These numbers are well below average. It could be that Brodeur's backups played on worse teams than normal - that is somewhat indicated by the low winning percentage. Even so, it is probable that the weighted results are closer to reality than the simple sum totals, for the reasons described above. The shot effect isn't as large, but the shot quality effect certainly shows up.

So, looking at these backup stats, can we make any conclusions about Brodeur? There could be other factors at play here, but the data appear to show a clear New Jersey shot prevention effect, with the goalies facing 2-3 fewer shots per game playing in New Jersey compared to everywhere else. They also stopped a higher percentage of shots, and won games at a much higher rate. The difference in shots against per game between Brodeur and his teammates was less than 1 shot per game in total, and almost identical when comparing the seasonal averages. That doesn't appear to provide any evidence for the theory that Brodeur can decrease shots against, but we don't know the typical difference in shots between a starter and his backups. The numbers given could be still be evidence of a slight effect if backups generally give up fewer shots than the starter, which may be a reasonable assumption based on a weaker strength of opposition and the team playing tighter defensively with a weaker goalie in the net. So for now, the results are still somewhat inconclusive, and further study is required to help identify and measure any goaltender shot prevention effects.

Tuesday, May 13, 2008

The Dominance of the Red Wings

I was browsing on Hockey Numbers' site looking at his always interesting expected goal numbers, and the numbers for Detroit are just eye-popping. I just wish that the TV broadcasting crews would look at these types of numbers before continuing to fall over themselves in praising Chris Osgood for his supposedly outstanding play.

Since Osgood became the starter, Detroit has allowed just 22.5 shots per game. These shots have generally been low quality shots, so the expected goals against have been just 11 goals in 8 games, according to Hockey Numbers. These are based on league averages, so you can do the math to figure out that a league average goalie playing Osgood's playoff minutes on Detroit should have about a 1.40 GAA and a .940 save percentage. Osgood's actual numbers: 1.47 GAA, .935 save percentage.

What about that 9-0 record? Is that impressive? It really isn't so hard to predict when you look at the numbers at the other end of the ice. Detroit has 37.2 expected goals in 8 games with Osgood as their starter (game 3 vs. Dallas hasn't yet been updated). That means with neutral goalies, Detroit wins pretty much every game 4-1 or 5-2. The Red Wings have been so dominant that the closest game in terms of expected goals that they have played since switching to Osgood was their 8-2 blowout in game 4 against Colorado.

Osgood has outplayed Dominik Hasek, but that is more an issue of time finally catching up with the Dominator - Hasek played a poor game 3 that cost Detroit a win, and was mediocre in game 4 when Nashville actually outplayed Detroit. But since the goalie switch Detroit's team play has improved, and they have been absolutely unstoppable at both ends of the ice. Maybe that can be attributed to Osgood's calming influence or something, but I really doubt it.

My intention is not to criticize Osgood, because he is not playing poorly. He is taking care of business, and I am sure Detroit is quite happy with merely decent goaltending. But it isn't my intention to praise him either, because he is not playing any better than the other goalies still left. Osgood is doing his job, just like, say, Brad Stuart is doing his job, or Kris Draper is doing his. The difference is that Osgood is wearing a different set of pads than the rest of his team, so he gets more credit for it.

Detroit isn't the first team ever to completely outplay their opposition in the playoffs, so it makes you wonder: How many other Osgood-types were there who became legends because of their playoff success on dominant teams? I'd wager there were more than a few.

Thursday, May 8, 2008

Carey Price

Carey Price has been getting some flak recently for his subpar performance in the playoffs against Philadelphia. Maybe Montreal should have kept a veteran goalie around, and maybe not. However, if people are making excuses that Martin Brodeur is tired, then what about Carey Price?

In the last 2 years, at the age of 19 and 20, Carey Price has gone through a major junior regular season, the world junior championships, major junior playoffs, the end of the AHL regular season, the AHL playoffs, NHL rookie camp, NHL training camp, NHL regular season with stints in the AHL, and the NHL playoffs. He played 82 games last year and 65 games this year, for a total of 147 games in all competitions over the last two seasons.

Price has been playing hockey basically non-stop for 18 months straight, most of it spent under the glare of the spotlight (world juniors, AHL playoffs, starting goalie in Montreal, NHL playoffs). Is it peculiar that at some point he gets burnt out or hits a rough patch? The battle against physical and mental exhaustion is why it is so tough for teams to make repeated deep playoff runs, and I think that was a major reason for Price's declining level of play. We'll see next season if he continues to improve and fulfill his promise as a franchise goalie; I expect that after a summer off Price will be just fine.

Tuesday, May 6, 2008

Top All-Time Goalies

I have been asked in the comments to list my top all-time goalies just as a reference point for my analysis on this blog.

My overall premise is that in the majority of cases, the goalie is as good as his team. When I evaluate somebody, I am looking for evidence that they were better or worse than the team around them. I don't care very much about things like wins or shutouts or Cups, as they are very strongly influenced by the team. Instead, I prefer to focus instead on save percentage, individual awards, playoff performance, performance relative to era, and performance relative to teammates.

All-time rankings are always a tough task because of different eras, incomplete historical information, uncertain team contexts, and other challenges, so it always comes down to a bit of guesswork. I am pretty settled on my top 4 guys, but after that I'm still trying to sort out the rest. I tend to think that ranked lists are very subjective and often not very meaningful (is there really a big difference between, say, the guy ranked 12th and 13th on pretty well any list?), so I present my top 4 ranked goalies along with a list of honourable mentions to others who are also in the argument.

1. Dominik Hasek

Most MVP awards by a goalie, most times finishing first among all goalies in MVP voting, highest career save percentage, best official single season save percentage, best ranking compared to his backup goalies, 6 Vezina Trophies.

2. Jacques Plante

Did very well compared to his backup goalies throughout his career. Played on some great Montreal teams, but his late career performance with St. Louis and Toronto was also outstanding. Has a very good playoff record. Won a Hart Trophy. Tied with Hasek for most times leading the league in "Goals Saved".

3. Glenn Hall

Named the best goalie in the league seven times in end of the year All-Star balloting, more times than any other goalie. Wasn't as outstanding in the playoffs, but his teams were likely a major factor.

4. Patrick Roy

The performances of his backups indicate that he was definitely helped by his teams, but Roy still has an impressive record: Excellent playoff resume, very good era-adjusted save percentage results, and 3 Vezinas and 3 Conn Smythes that suggest a strong individual contribution to his teams' success.

Other goalies I think were very good include: Bernie Parent (very high peak value), Ken Dryden (not completely sold on him because of the huge team effect, but his performance numbers are outstanding), Turk Broda (exceptional playoff performer), Tony Esposito (great regular season play makes up for lack of playoff success), and Johnny Bower (did well in save percentage stats put together from the Original Six era).

Monday, May 5, 2008

Divergence in Goalie Opinions

I was reminded of the wide range of opinions on goalies while going through a few HF Boards threads recently. There are many different opinions on which goalies are good, which are the best, and especially which are the best of all-time. What is more interesting is that when someone tries to claim that one goalie is clearly superior to another, they often get shouted down by others who claim that "everyone has their own opinion" on the matter.

I somehow don't think it would become just a mere matter of divergent opinion if someone went around claiming that Jean Beliveau or Rocket Richard was the greatest player of all-time. Virtually every all-time player ranking I have ever seen had a top 4 that was one permutation or another of Gretzky, Orr, Howe and Lemieux, with either #99 or #4 always coming out on top. But I could claim a different all-time best goalie for every day of the week (say, Roy, Hasek, Brodeur, Hall, Plante, Sawchuk, Dryden), and I could find people who would agree with me on each one.

This is just more evidence that goalie evaluation is very subjective and very unrefined, and why there are many observers that continue to try to develop tools that more accurately capture and evaluate a goalie's true level of achievement.