Tuesday, September 18, 2007

Shots Matter

James Mirtle presented a fine and finely detailed look at some goaltending history in this post. Being the sort who has a certain fascination with the behavior of numbers, The Peerless offered a comment, which we share with you below:

Thanks for that excellent look at goaltending trends. One of the things that has occurred to me, anecdotally, is that shots matter from a defensive point of view. At this level of play, there just isn't that much difference in save percentage among goaltenders in the NHL (last year, the top 20 goalies in save percentage with at least 50 games ranged from .902 to .922).

But looking at one goaltender to whom I pay attention -- Olaf Kolzig of the Capitals -- the effects of shots is telling. Kolzig faced 1,771 shots last year (33.4 shots per 60 minutes of play). For his trouble, he had a goals against average of 3.00, 20th in the league among goalies with at least 50 games, while posting a .910 save percentage. In order to shave that GAA to, say, 10th (2.58, Rick DiPietro) facing the same number of shots, Kolzig would have had register a save percentage of .923. Had he done so, he'd have led all goaltenders who played 50 or more games in that statistic.

Here is another way to look at it. Marty Turco and Kolzig had the same save percentage in the regular seson (.910). But while Kolzig had his facing 33.4 shots per 60 minutes, Turco had his facing 24.9 shots per 60 minutes. The arithmetic results in a 0.77 differential in their respective GAA (more than 25 percent better in Turco's case). Which team's goalie -- and team -- was more successful?

That's a long way round to the point that "shots" seem the most underrated statistic in the sport. Which brings to mind another factor in this -- what has been the trend in blocked shots and missed shots? And, have goals scored as a share of "shots taken" (as opposed to "shots on goal") changed over time?

We're mindful of a rather standard response to the "shots" argument, that there are "shots" and there are "shots." By this we mean that goaltenders might face a lot of easily stoppable shots that inflate a shots on goal statistic. In any given game, that is certainly possible, but data being what they are over a series or a population, we suspect that over the course of a regular season that sort of thing evens out -- that the 6-8 easy shots goaltender A might face today are evened out by a similar number goaltender B faces next week or goaltender C faces next month.

I think it useful to pay particular attention to the comparison of Kolzig and Turco, above, and apply the analysis we used in the first example. For Kolzig to have achieved Turco's GAA (2.23) while facing the number of shots he did last year, he would have had to post a save percentage of .933. That would have led all goaltenders, according to the NHL's statistics. And Turco finished fourth in GAA.

Wayne Gretzky famously said that you miss 100 percent of the shots you don't take. It's merely another way of saying, "shots matter."

8 comments:

Anonymous said...

Peerless:
I like the Turco/Kolzig comparison because it shows the value that a defense-first team adds (or subtracts, in this case) to the GAA. In other words, with Zilla backing up the Stars Olie would have led the league in GAA, and would be mentioned in the same breath as Roy and Brodeur.

Bradley said...

I think another thing that's interesting to think about, though, is that last season I believe Olie played really well when facing something like 40 or more shots per game (IIRC you had produced a statistic to that effect in an earlier post). So, on the one hand, bringing Olie's shots closer to Turco may help his stats, you can't ignore how well he seems to play when he gets a big workout. What this is leading me to, really, is that it's not just the number of shots that matter, but the quality of shots. If Olie is facing 50 easy shots every night, then his stats could be amazing; facing 20 shots from dangerous areas could very well destroy him so to speak. Since there isn't really a good way to create a "shot quality" stat (and what a pain it would be to go back and look at where all those 1771 shots were taken from), it is tough to do too much analysis (at least on a game-by-game basis) about how important shots are to a metric like GAA.

Anonymous said...

IIRC, Olie's workload during the '98 Cup run was pretty staggering in terms of shots faced.

The Peerless said...

You're always going to find games, or even stretches of games when a goaltender (including Kolzig) will have a Herculean effort in the face of w withering barrage of shots.

It is not something from which a trend should (or even does) develop. Over the course of a season (or, put another way, a population of contests) these things tend to "even out." All other things considered, it is better to face fewer rather than more shots over an 82-game season.

The Peerless said...

Also, on the matter of statistics on quality or types of shots, I suspect if any such analysis has been done, it would have been done by this fellow:

http://forechecker.blogspot.com/

Anonymous said...

The law of large numbers would indicate that it is better over time to face fewer shots, undoubtedly, without taking account the quality of said shots. No team can consistently field a blueline of Larry Robinsons or Rod Langways, therefore, shot quality will trend toward a norm.

Shmee said...

I just about died of laughter when I saw your banner. Thats my dad over Olie's shoulder...I finally got him to go to a game with me, and he was rewarded by a great Caps win, PLUS a big picture in the WaPo Express the next day. The person who's head is cut off in the banner is me:)

Joe said...

-450

This is difference in shots on goal the Caps faced last year. That's almost 5.5 shots per game. This stat is important for a couple of different reasons. First, it shows the how much pressure the opposition was putting on our goaltenders and young defense. Secondly, it shows that our offense was not able to keep the pressure on the other teams defense. The good news was that the Caps shooting percentage was slightly above the opposition. The off-season moves the Caps made this summer seem to address the need to change this trend. The acquisition of puck possession forwards and an offensive defensemen, in theory, will help to reduce this deficit. The more time the Caps can spend in the offensive zone means less shots on Olie and less pressure on the defense to make stops. It also forces the opposition to expend more energy and gives us more opportunity to put points on the board. There has been a lot of noise made that the Caps did not sign a stud stopping defensemen, but the Caps seem to be going with the philosophy that more offense is good defense. Doing this also allows the younger defensemen to develop without being under siege all the time giving them time they need to develop some confidence. I don't know how many times I watched games last year where I saw our offensive weakness turned into defensive struggles. It seemed like we were always running around in our own zone. Will this pay off? I hope so because I am a believer that putting more pressure on the other team and forcing them to stop you is a much better strategy than merely trying to match the opposition. Its also a lot more fun to watch when you believe your team is going to try and score every time they get the puck because we definitely have some finishers on our team.