Tuesday, September 23, 2008

The Continuing Shots Against Investigation

I compared shots per game averages for starters to backup goalies during the 2007-08 season, and was a bit surprised to find that over half the league had a substantial difference in shots faced averages between the #1 and #2 goalies. Sixteen out of the 30 teams had a difference of 1.5 shots per game or better between the starter and the backup, with a few more teams just missing the cutoff at 1.3 or 1.4. So having a sizeable shot differential was not rare but commonplace around the league last season.

I decided to look at just the teams with a substantial shot differential, using 1.5 as a cutoff, trying to isolate any variables that could explain the differences. I broke it down first by starter vs. backup (again using the goalie with most games played as the starter):

Starter: 29.3 SA/60, 26.8 SA/60 5 on 5, 43.2 SA/60 4 on 5
Backup: 29.3 SA/60, 26.1 SA/60 5 on 5, 41.1 SA/60 4 on 5

I also looked at two different measures of shot quality, both from Behind the Net and Hockey Numbers. Behind the Net gives the expected save percentage for each goalie based on the shots they faced. Hockey Numbers gives only the shot-quality neutral save percentage, but we can calculate the expected save percentage from that number. Behind the Net had starters and backups almost equal at .908 and .907 respectively. Hockey Numbers had a bit more of a gap, with starters facing slightly easier shots (.907 expected save percentage compared to .903 for the backups).

Other than the penalty kill discrepancy noted earlier, there isn't much difference there.
I then broke it down into the goalies with high shots against averages compared to those with lower shots against averages.

High shots: 30.7 SA/60, 27.9 SA/60 5 on 5, 42.6 SA/60 4 on 5
Low shots: 28.0 SA/60, 25.1 SA/60 5 on 5, 41.1 SA/60 4 on 5

There is a significant even-strength gap that is driving the results. Let's look at the shot-quality numbers for this group:

High shots: .908 (BtN), .908 (HN)
Low shots: .908 (BtN), .904 (HN)

The goalies who were facing more shots per game were not facing more difficult shots. Again, this does not imply that the extra shots they were facing were rebound shots or other prime scoring chances.

However, those extra chances did have an effect on goals against. The GAAs for the two groups were almost identical, although it was actually the goalies facing more shots that had a slightly lower GAA (2.78 to 2.80). They did much better at stopping the puck by both shot-quality measurements (.30 better in Behind the Net's GAA above average, and .006 better in SQNSV%), but the extra shots they faced resulted in more goals against.

There were two other things I looked at: shots for, and missed shots. Surprisingly to me, the backups had more shots for than the starters, and the goalies facing fewer shots against had more shots for than the goalies facing more shots. Starters had just 25.9 shots for/60 at even-strength compared to 26.7 for their backups, and the teammates of the high shot goalies took 26.1 shots/60 compared to 26.4 for the low shot goalies.

The starters and the backups were very close in missed shots, both at even-strength (10.9 and 11.1) and at 4 on 5 (18.8 and 18.7 respectively). In the high vs. low shot comparison, missed shots were very close at even-strength (10.8 to 10.9), but there was a bit of a gap at 4 on 5 (18.2 to 18.8).

I looked at the numbers for 2006-07 for high shot vs. low shot goalies, and they confirmed the basic principles: the goalies facing more shots tended to have better save percentages (.918 to .914 at even-strength, unadjusted), but the GAAs were almost identical on average (2.89 and 2.88).

So nothing really jumps out as a cause for the shot discrepancies. That these differences were found league-wide makes me think that a lot of it might be random noise, and it is unclear how much of the gap is repeatable from season to season. That is the key question: did the guy who is outperforming his teammates in terms of SA/60 also do it last year, and is he likely to do it next year? I think it is still very difficult to tell which goalie is allowing fewer shots than the other. Try this little quiz: I put together a list of 10 goalie tandems who had a difference of 1.5 or greater in their shots against averages in 2007-08. Guess which of the two goalies allowed fewer shots per game. If you score better than 50% you are outperforming me (I'll post the answers in the comments):

Cam Ward or John Grahame?
Ryan Miller or Jocelyn Thibault?
Tim Thomas or Alex Auld?
Chris Osgood or Dominik Hasek?
Niklas Backstrom or Josh Harding?
Carey Price or Cristobal Huet?
Chris Mason or Dan Ellis?
Martin Gerber or Ray Emery?
Marc-Andre Fleury or Ty Conklin?
Olaf Kolzig or Brent Johnson?


Bill Morran said...

I'll say Grahame, Thibault, Auld, Hasek, Harding, Ellis, Emery, Conklin, and Johnson.

Had I not got the feeling that these tandems were picked for a reason, I probably would have said Grahame, Miller, Auld, Hasek, Harding, huet, Ellis, Gerber, Conklin, and Kolzig.

The Contrarian Goaltender said...

Bill, you got 4 out of 10 right on both of your guesses.

I didn't pick them for a reason, there were 16 that met the criteria and I picked out what I thought were the 10 best-known tandems. I intentionally omitted Lehtonen/Hedberg, since we've already dicussed them, and Toskala/Raycroft, because Raycroft is so terrible I thought that one would be pretty obvious. The other 4 all involve probably lesser known goalies (DiPietro/Dubielewicz, Holmqvist/Ramo, LaBarbera/Aubin, Leclaire/Norrena). Any of those could have been used instead, though, so if you want to take a crack at those ones as well, go ahead.

Bruce said...

Here's my guesses for the guy with fewer shots: Ward, Miller, Auld, Hasek, Backstrom, Price, Mason, Emery, Fleury, Kolzig.

Of the others: Hedberg, Toskala, DiPietro, Holmqvist, Aubin, Leclaire. A couple are guesses cuz as you suggest teams like LA and Columbus weren't featured on the tube too often, but a few of them are slam dunks (DiPietro v. Dubliewicz probably being the extreme).

The Contrarian Goaltender said...

Well, Bruce, I am impressed. Very impressed. You went 8 for 10 (the only guys you missed on were Miller and Price), and then 3 for 4 on the bonus questions (missed on Leclaire).

Did you go based on who you thought was the better puckhandler? Or some combination of overall goalie play?

By the way, DiPietro-Dubielewicz did have an extreme gap (4.4 shots per game difference), but it wasn't the biggest gap - Aubin faced 5.3 shots per game fewer than LaBarbera. Of course both of those backups didn't play many games so it is more likely those results would be extreme.

Bill Morran said...

Fleury shocks me more than any backup. I've always hated him.

By the by, I've never commented on this blog before today, so I'm just going to mention I read this every day, and love the analyzed statistics, instead of getting a "who won more games?" argument when talking about a better goaltender.

But it applies in all sports. I'm so tired of an Eli Manning winning a Super Bowl, and then people decided he's a Super Star. Brad Johnson won a Super Bowl. Chris Osgood won a Stanley Cup. Get over it.

I was just wondering what your thoughts on Mike Richter were?

The Contrarian Goaltender said...

I find it a bit tough to place Richter, actually. There's a lot to like: His overall numbers are fairly strong (career save percentage .904, league average throughout career .898), he pushed a prime Vanbiesbrouck out of town early in his career, and his playoff numbers are good. On the downside, he could be inconsistent year to year and he had virtually no awards recognition (only 1 first-place Vezina or First Team All-Star vote in his entire career). I guess the key question is just how good was the Rangers defence, but I think I would have liked to have seen Richter outplay his backup goalies by a bit more if he was really was elite.

My subjective viewpoint of Richter was that when he was on his game he was as unbeatable as anybody this side of Hasek. I'm not sure there is enough in his career to put him among the very best of his generation, but I think he is somewhere in the second tier of good starting goalies. But I'd like to take a closer look at Richter to try to find out exactly where he ranks against his peers.

Also, to tie Richter back to the present discussion, he apparently gave up a lot of shots compared to his backup goalies. Did his athletic, reflex style result in more rebounds? I don't know.

The Contrarian Goaltender said...

By the way, I looked at the 2006-07 numbers to see if any of the above-mentioned goalie tandems were still intact and how they did. Six of them were, and interestingly enough most of them had substantially different results.

Lehtonen/Hedberg and Osgood/Hasek still had a big shot gap in the same direction, but for the other 4 there was not only a much smaller differential, it actually went the other way every time, i.e. the goalie that faced more shots in 2007-08 faced fewer in 2006-07 (Ward/Grahame, Leclaire/Norrena, Gerber/Emery, Kolzig/Johnson). Also, Dubielewicz had cups of coffee with the Islanders in both 2005-06 and 2006-07, and both times he ended up with fewer shots faced per game than DiPietro, but we are talking about really small samples (<400 minutes). So I'm more open to the possibility of sustainable, statistically significance shot prevention effects by goaltenders, but I still think most of the variance is just random noise.

Bruce said...

Did you go based on who you thought was the better puckhandler? Or some combination of overall goalie play?

Both. The more aggressive sweeper-type goalies tend to keep play away from the goal mouth through puckhandling and other means like rebound control, but the skill sets don't entirely overlap nor are they mutually exclusive. e.g. Hasek, who for all his puckstopping wizardry could be recklessly aggressive in racing to loose pucks to (mostly!) prevent shots.

All things being equal I'll pick the guy who plays deeper in his net to invite more shots. The book on some of these guys is to shoot from anywhere, sometimes a 35-footer has a better chance of finding a hole than a five-footer. Which is at the root of my skepticism of both Sv% and SQNSv% as a truly accurate measure of goaltender performance. Both are good, neither is perfect.

Of the ones I got wrong I was most surprised by Huet, who has always had an outstanding Sv% but relatively high shots against (a not uncommon combination). So at first blush he's of the Roberto Luongo School of Stoppers. Looking now at his actual numbers, it's instructive to compare his last two seasons in Montreal:

2006-07: 2286 MP, 1280 SA, .916 Sv%
2007-08: 2278 MP, 1150 SA, .916 Sv%

That's fully a reduction of 10% in virtually identical ice time. How much of that was due to changes in Crystal Ball's game and how much due to, say, Souray-out-Hamrlik-in, is difficult to quantify. The "lumpers" might write it all of to team effects, we "splitters" might say Huet is getting better, and smarter, as he gains experience, and is becoming more proficient at helping out his defence.

I'm still shocked that Washington didn't re-sign him.

The Contrarian Goaltender said...

I agree with you about Huet, I think he would have been a much better bet than Theodore. Huet couldn't have had a much better audition for the job either (11-2-0, 1.63, .936), and they still opted to save $1.5 million and bring in another guy.

The book on some of these guys is to shoot from anywhere, sometimes a 35-footer has a better chance of finding a hole than a five-footer.

If there is a difference, I think this is it. I don't think the number of rebound shots is high enough to account for much of a difference, and the shot quality measures, which are mostly based on shot distance, are often very similar for goalies who have fairly large shots against discrepancies. So either NHL shooters think it is smarter to fire away at certain goalies rather than others, or otherwise perhaps certain goalies help their teammates clear the zone faster, so they face fewer but not easier shots?

I just found out that the NHL tracked zone times for the 1999-00, 2000-01 and 2001-02 seasons and published them on their game sheets. I think I'll take a look at a few pairings with large shot differentials and see if time spent in the defensive zone varies at all. If anyone has any suggestions of guys for me to look at, let me know.

Anonymous said...

"The book on some of these guys is to shoot from anywhere, sometimes a 35-footer has a better chance of finding a hole than a five-footer. Which is at the root of my skepticism of both Sv% and SQNSv% as a truly accurate measure of goaltender performance."

Does a goalie exist who has a lower SV% on shots from 35 feet away vs. 5 feet away?

Doesn't shot-quality incorporate shot location (among other things)?

Bruce said...

Does a goalie exist who has a lower SV% on shots from 35 feet away vs. 5 feet away?

Probably not, Anon. But there may be goalies against whom you might do better firing three 35-footers than trying to work the puck in for one five-footer. Or three bad angle shots vs. one from the slot.

Doesn't shot-quality incorporate shot location (among other things)?

I think it calculates distance from the end boards, but not from the side boards. Not all 17-footers are created equal, in other words.

Anonymous said...

from watching brodeur i would think if anyone qualifies for the statement above about shooting from 35 ft out, or bad angles, its him. this is esecially noticeable around playoff time the last 3 years. as a devils fan i have seen just about every game, and its there in the regular season, but even more apparent during the post season. its frustrating because he'll stop the shots in the slot, or the side to side one timers, rarely gets beat on a break away, and but then gives up these kinda goals. i know vs the rangers last year, jagr's goal in game one, forget the dman in game 4, then the year before against the senators he gave up a bunch from sharp angles especially 5 feet out from the goal line by the outer hash marks.

Bruce said...

from watching brodeur i would think if anyone qualifies for the statement above about shooting from 35 ft out, or bad angles, its him. this is esecially noticeable around playoff time the last 3 years.

Anonymous#54321: An interesting observation. Is this anecdotal evidence on a couple goals here and there that ticked you off, or do you feel this is a systemic change of Jersey defensive strategies or opposition tactics?

If the latter I wonder if the book on Marty has changed since the lockout? He has had both a) more shots and b) a higher Sv%, both of which are consistent with teams shooting from outside a little more. Judging from his (regular season) GAA, it hasn't exactly been working, whatever they're trying.

The Contrarian Goaltender said...

Interesting comment, Anonymous. That agrees with my subjective viewpoint. It seems like Brodeur gets beat on close-in, bad angle shots more often than a lot of goalies. I think overall Brodeur is more likely to make the tough save and then give up a softie, something which I think tends to make a goalie look better than he is. I guess you could call it the Grant Fuhr Perception Bias - you watch a guy make a few highlight reel saves in a game and that is what tends to stick in your mind, rather than the fact that he stopped, say, 21 out of 24 shots total.

There is some evidence that indicates Anonymous is right. If you look at the way Hockey Numbers breaks down the type of shot against (easy, medium, difficult), Brodeur ranks as the best in the league against difficult shots and mid-pack against medium scoring chances. I believe the results were pretty similar last year as well.

Re: Bruce's comment on shot selection, I don't think the shooters are doing anything different, I think New Jersey is just letting more shots through. The Devils' shot quality numbers have dropped substantially over the last few seasons, which indicates that the average shot distance is decreasing, not increasing.

There is one shot quality measurement that is based on both distance from the net and distance from the sideboards (Behind the Net). According to that measure, Brodeur had an expected save percentage of .906, which is right at league average. The other shot quality measurements based only on distance agree that New Jersey was pretty much average in shot quality in 2007-08. So Brodeur probably isn't facing many more sharp angle shots than average, but maybe he should be.

Unknown said...

So what are the answers?