SHOT QUALITY
SHOT QUALITY AGAINST
Do teams with higher SQA (i.e. worse) really give up more dangerous shots against, or is it merely an artifact produced by arena bias or some other element of the measurement process?
If teams with lower save percentages tend to have higher SQA, then that’s fairly solid evidence that shot quality is measuring something genuine.
There is a negative correlation between SQA and save percentage at the team level, meaning that, on average, the teams that give up more dangerous shots against tend to have lower save percentages.
a team’s SQA for any given season is highly correlated with the values for both the preceding and following seasons, and that this relationship does not appear to be mediated by arena bias.
Based on these findings, SQA can be defined as:
· A real measurement of the average relative dangerousness of the shots allowed by any given team, as manifested in the lower team save percentages of teams that allow relatively more dangerous shots on average.
· A reliable, enduring element of team defense, as manifested in the substantial inter-season correlation at the team level.
SHOT QUALITY FOR
If the shot quality data is actually measuring what it purports to, then there should be a positive correlation between SQF and shooting percentage at the team level.
Thus, just as SQA is a reliable and valid component of team defence, so too is SQF a valid and reliable component of team offence.
SHOT QUALITY AT EVEN STRENGTH
there is little team-to-team variance in shot quality against at even strength. Can that be correct?
There is a persistently higher variance for goalies who move to different teams than those who play on the same team, suggesting that team situations are not equal.
most teams are pretty close in terms of difficulty of shots allowed.
Most teams face a similar range of shot quality at even-strength
There does appear to be some significance to shot quality for 5 on 5 play.
for the most part, even strength shot quality is pretty consistent in the NHL.
BIGGEST INFLUENCE ON SHOT QUALITY
(Aug 2009)
The two biggest factors that influence Shot Quality are the distance at which the shot is taken and the game state.
Given that different shots at different distances have different success rates, and that the aggregate distances allowed by different teams vary, there is every reason to believe that there might be shot quality differences in the aggregate as well
More importantly, on a team-by-team basis, shot quality does correlate both with shooting percentage and inversely with save percentage, as it should
POSITIONAL SHOT QUALITY
(Sept 04, 2009)
A good amount of evidence exists that offensive players can, in fact, display the ability to take higher quality shots than other offensive players. I.e., shooting percentages for certain players are persistently higher than can reasonably be explained by chance
Further, we observe a large difference in shooting percentages between forwards and defensemen.
forwards shot 9.6 percent at even strength last season, and defensemen shot 4.1 percent.
FORWARDS VS DEFENSEMEN SHOT QUALITY
(Sept 17, 2009 – F vs D SQ)
So, given the same opportunities as defensemen, forwards had a shooting percentage that was 14% higher.
Fundamentally, forwards are selected for their offensive ability, and the unsurprising outcome here is that they do in fact have better offensive abilities, which includes taking higher quality shots than their defensemen counterparts.
DOES SHOT QUALITY EXIST (AND CAN IT BE MEASURED)
(April 23, 2010)
5 factors that were statistically significant that affected a shot’s level of danger:
· The distance from which the shot was taken
· Whether or not the shot was a rebound (defined as a shot taken at less than 25 feet within 2 seconds of a previous shot)
· The manpower situation (even-strength, power-play, short-handed), whether the shot was taken
· Shots taken immediately after a turnover
· The shot type.
Of these 5 factors, the first 3 were very important, while the last two were marginal.
Shot quality correlates negatively with shot volume
The best shot quality teams tend to get outshot significantly, while the worst shot quality teams are all shot-positive.
THE SHOT QUALITY PRIZE
(Jan 2011)
If shot quality doesn’t affect shooting percentage, it doesn’t exist, at least in the way that most of us understand “shot quality”.
many individual shots are much dangerous than others, but in the aggregate the difference between all shots taken/allowed at even-strength by team 1 and team 2 is small
Shot quality should correspond with scoring chances. If you find a significant difference between tracked scoring chance % and Fenwick , that’s shot quality
WHY I HATE SHOT QUALITY
There is a limit on what we could hope to learn from "shot quality" and save percentage was dominated by luck.
PDO – simply the sum of shooting percentage and save percentage – is also almost entirely luck.
Vic also showed that individual shooting percentage also regressed very heavily toward a player’s career averages.
I’d like to move past shot quality as such a frequent focus of analysis because I don’t think it’s going to return much for all of the effort.
There are dozens of things an NHL team should chase before they start looking for finishing talent
OUTSHOOTING + OUTFINISHING >> SHOT QUALITY
(Oct 2011)
What Gabe is suggesting is that players have little or no ability to generate goals aside from their ability to generate shots. Those who follow me know that I disagree
If shooting percentage were indeed random we would expect some Moen and Pahlsson types to be intermingled with the Sedin’s and Crosby’s, but generally speaking they are not.
Shot Quality only represents a small fraction of this advantage; outshooting and outfinishing are the largest contributors
The ability to generate shots from more difficult locations is a minor factor in being a better player but both being able to take more shots and being able to capitalize on those shots is of far greater importance
It is fair to suggest that scoring goals is ~40% shot generation and ~60% the ability to capitalize on those shots (either through shot location or better shooting percentages from those locations).
The Conclusion: There simply is no reliable way of evaluating a player statistically at even a marginally high confidence level using just a single year of data. Our choices are either performing a Corsi analysis and doing a good job at predicting 40% of the game or performing a goal based analysis and doing a poor job at predicting 100% of the game. Either way we end up with a fairly unreliable player evaluation.
HOW MUCH DOES SHOT QUALITY MATTER
most shot quality effects are smaller than people think, and that over the sample sizes we normally work with, differences in shot quality tend to be dominated more by noise than talent.
Team Level Shooting Percentage
Even after 82 games, about 2/3 of the shooting percentage differences between teams comes from simple variance.
· “The point is: “Differences in shooting percentage are small and require a very large data set to overcome noise, so you won’t be wrong by much if you ignore them.”
players’ shooting percentages vary a lot from year to year, and you should look at several years’ stats to estimate how a player will shoot going forwards.
differences in shooting talent are significant and require a very large data set, so look at several years of shooting percentages to make your predictions.”
Remove the tendency of good shooters to play together, and it looks like over multiple seasons we see only a few top playmakers improving their teammates’ shooting.
· The point is: “The ability to improve teammates’ shooting is small and requires a very large data set to overcome noise, so you won’t be wrong by much if you ignore it.”
The result is that any team effect on a goalie’s save percentage doesn’t add up to more than a goal or two per season.
“Differences in shot locations are small and require a very large data set to overcome noise, so you won’t be wrong by much if you ignore them.”
Conclusion
Together, Fenwick/Corsi and Luck account for around ¾ of team winning percentage. What’s the remainder? Goaltending talent – which Tom Awad estimates at about 5% - and special teams, along with a very small sliver that’s due to shooting talent and the oft-mentioned “shot quality.”
In general, shot quality factors tend to be small enough that they don’t grossly alter our understanding of the game, and they tend to be swamped by noise during in-season analysis.
SHOT QUALITY EXISTS
(Aug 2012)
In short, it is very unlikely that Crosby and Kennedy would have those on-ice shooting percentages based on luck alone.
So essentially there is no chance that that happens based on luck alone. Shot quality of some sort is a factor. There is definitely shot quality skill/talent factoring into the equation
SMALL VS LARGE SAMPLE SIZES AND SHOT QUALITY
shot quality has an enormous impact on the level of an individual shot.
Over a small sample – like a game, a playoff series, or even a season from a particular individual – the gap in shot quality could still easily be quite large.
Over large samples – like a full season – this becomes less likely. The research done so far suggests that, at the team level, this can be a repeatable skill. Of course, in the middle of a season, there would be so many false positives (obligatory mention of the 2011-12 Minnesota Wild) that you wouldn’t want to bet on any one particular team sustaining their advantage in the percentages the rest of the way.
And what about the individual level? It’s fair to say that the consensus is that it’s very difficult for us to demonstrate talent statistically.
But we shouldn’t always be quick to jump to the “luck” conclusion when a player is under of over performing
THE SHOT QUALITY PROJECT
(Oct 22, 2013)
Alan Ryder’s study confirmed distance as being a determining factor in goal probability.
Clean Shots:
Clean shots account for 85 percent of a goaltender’s workload, yet only 50 percent of the goals and an average save percentage of .951 and the fluctuation was very light (ie. Any goalie can save a clean shot).
Contrast that to the .693 save percentage on transition shots and it’s pretty clear that a goaltender exposed to more transition opportunities has tougher job.
It is quite clear that scoring success in the NHL is predicated on movement and deception. If you remove these elements even the worst goaltender in the league begins to look like Dominik Hasek.
Transition Shots:
Variability was much higher – 23% vs 3% for clean shots.
Deflections, Redirections, Tips:
The average save percentage on a deflected shot registered as .736. The gap between the best and worst results was 270 goals per 1,000 shots.
Almost every deflected puck results in a defined scoring chance against.
Rebounds:
The average save percentage on a rebound shot registered as .760.
INDIVIDUAL SHOT PROBABLILITY AND AVERAGE SHOT PROBABILITY
Individual Shot Probability does matter and this has been illustrated time and time again. There’s no doubt about it.
What has not been shown to matter much, to my mind, is Average Shot Probability (ASP), either for shots that a goalie has faced or that a team has faced or that a team has generated over a long period of time. ASP, matters but not a ton.
WHY SHOT QUALITY IS NOT THAT IMPORTANT
Shot quality exists but the amount of variance effects in shot location makes it difficult to determine how much of shot quality is skill and how much is chance.
while shot quality differences exists- it does not add overwhelming increases in discovery to shot metric analysis.
In general, shot quality factors tend to be small enough that they don’t grossly alter our understanding of the game, and they tend to be swamped by noise during in-season analysis.
Shot quality by shot location shows a difference in the goals against a team expects. The difference for the most part is quite small and doesn’t quite align in any general trend with expectations.
QUANTIFYING SHOT QUALITY
If shot quality exists as a repeatable phenomenon, there would seem to be three mechanisms at work that we’d have to account for. The first is the “pure talent” effect mentioned above: if you happen to have a player with an unnatural talent for shooting the puck
The second is a usage effect: if your coach gives your more talented shooters more ice time and more favorable zone starts, they’ll end up taking more of the team’s shots, which would imply a higher team Sh%.
What many have wondered about is the third mechanism, which for lack of a better term I’ll call the “Secret Sauce” effect: by this, teams shoot a higher percentage by means not accounted for by either talent or deployment.
As such, there does not appear to be a meaningful shot quality effect broadly across the NHL. In other words, if a team is shooting a high percentage, it’s because the players as a group are doing so, not because of anything at the coaching/system level. Which would be okay if those players were likely to sustain those individual percentages. Unfortunately, as we’ve seen elsewhere, that isn’t likely for most players.
None of the President’s Trophy winners or Stanley Cup champions in any of these seasons showed evidence of a shot quality effect.
Perhaps more importantly, none of the teams leading the NHL in goals in these seasons showed evidence of a shot quality effect. It looks as though those teams achieved what they did by having talented shooters and putting tons of shots on goal, rather than boosting Sh% through usage or any other mechanism.
EXPLORING THE THEORETICAL LIMITS OF SHOT QUALITY https://web.archive.org/web/20141019010135/http://www.hockeyprospectus.com/exploring-the-theoretical-limits-of-shot-quality/
(June 2014)
The barrier between shot and goal based statistics is called shooting or save percentage.
By predicting the chances of any one shot going in, we don’t need to rely on the small sample size ‘true’ shooting percentage gives us.
The goal of this analysis is to see how good of a model we can create to accurately reflect the ‘true’ chances of a shot being scored, using only the data the NHL provides
On average, shooters are about 1.7% in shooting% away from their expected shooting%.
1. A player’s shooting skill, above the variables described in the model, is worth about 1.6% per shot.
2. Expected shooting% is a repeatable statistic at the season level, and it has more predictive power then raw shooting% season to season.
HOW IMPORTANT IS LOCATION IN SHOT QUALITY
there are two aspects of shot quality. These are, the quality of an individual shot and the average shot quality of all shots taken by a team or a player when on the ice.
I have always claimed that shot quality exists in the Average Shot Probability sense of the word.
There are even teams that have consistently posted above or below average shooting percentages. Shot quality in the Average Shot Probability sense exists and we must acknowledge that.
Relatively little indication that shot location varies across teams in a significant enough way to have a significant impact on shooting percentage.
The greatest spread in talent between first tier players and fourth tier players is being able to out finish your opponents followed closely by outshooting your opponents. Having a better average shot location is a relatively minor factor in what makes good players good. A key takeaway is average shot location has relatively small impact on average shot probability which is consistent with what everyone has found.
HOW IMPORTANT IS LOCATION IS SHOT QUALITY
xG is literally the most direct way to measure shot quality that exists, given the current data. Unless there is a way to measure the information about where the puck was moving prior to the shot, you’re not going to squeeze anything more out of the current data.
Honestly, even with richer data, the improvements to existing shot quality models are going to be small increments. There are no leaps to be had,
We know shot quality exists. Shootout shooting percentage is higher than PP shooting percentage which, in turn, is higher than 5v5 shooting percentage. It is completely, abundantly obvious that shot quality exists.
the impact of contemporary coaching basically creates an environment where generating shot quality is hard. The NHL is hockey being played by generally comparable players, within generally comparable systems.
The contextual qualities of the shot, like distance, angle, puck movement, screening, whether it’s a rebound, etc. are much more a product of collective offensive system and player creativity than of individual shooter skill. Shooters impact aim and velocity.
We already know that the impact of shot quality (context + skill) is miniscule in comparison to other factors,
what we think of as shot quality is actually a function of the defense and not the shooter.
shooting % for dmen is mostly related to how well they short the zone, not how hard they shoot.
Shot Quality exists, but the impact is small so you can ignore it for the most part.
SHOT QUALITY EXISTS AND IS IMPORTANT
Shot quality definitely exists. Some shots are definitely more difficult to save than others. Those who want to minimize the importance of shot quality go by the premise that over the long haul the average shot quality of all the shots taken when a player is on the ice or a whole team over the course of a season will average out to pretty much the same value for all players and teams. The claim is that shot quality exists for a single shot, but for a collection of a large number of shots during which a player is on the ice there just isn’t much variability.
The answer to this is simple. The most direct measure of shot quality will be shooting percentage
I believe that existing models overallocate the variance in observed shooting percentage to luck and under allocate it to talent in maintaining a higher than average shot quality (or lower than average for those who lack talent).
Shot quality exists. It is incredibly important. It is a big reason why good players are good players