“A statistician is concerned what baseball statistics ARE. I had no concern with what they are. I didn’t care, and I don’t care, whether Mike Schmidt hit .306 or .296 against left-handed pitching. I was concerned with what the statistics MEAN.” – Bill James
It is a standard of today’s sporting world that we see a lot of stats throughout a broadcast. In addition to the standard goals and assists, we see plenty during hockey games. Blocked shots numbers, penalty kill percentage, a team’s average age. What does not seem to come up too much is: So what?
How much do penalties actually hurt a team? If my team blocks a lot of shots that means they are great defensive team, right? Physical play is vital to success! Why aren’t they hitting more guys!? Based on the games I have watched, it would be reasonable to assume these things matter. I have never heard an announcer advocate shying away from physical play or scold a defender for putting his body between the goal and a shot.
But here’s the thing… On average, teams who block more shots allow more goals. More penalty minutes has a negligible effect on goals allowed. And there is no connection between the number of hits a team dishes out and how successful they are. Knowing what the numbers are means nothing if we interpret them wrong.
Descriptions and Predictions
We need to be conscious of which stats are descriptive and which are predictive. Most stats are descriptive because they tell us what has already happened: Alex Ovechkin scored three goals in his last game. The danger comes in when we imply stats like this have some sort of predictive power: Ovechkin is on a roll right now, he scored three goals in the last game. That is a redundant statement. He is “on a roll” because he scored three goals in his last game, but saying he is “on a roll” is hinting that he will maintain his high level of play in his next game. He could score three goals, or zero, what he did last game does not matter.
This is similar to statements thrown around all of the time like, “This team needs to be more physical in the second period.” It’s subtle, but the implication here is that being physical will lead to greater success. Is that true though?
There won’t be much math here, but to give you a sense of what we are looking at, let’s find the correlation coefficient (or R-squared) between our two factors. For example, we would expect teams with a high goal differential (goals scored – goals allowed) to do well. If we graph the two over the last three full seasons, we get this:
(Click on graphs to embiggen.)
Things are as we expected. As goal differential goes up, team points go up. More importantly, our R-squared is 0.87. The closer R-squared is to 1, the stronger the two values are connected, conversely if it is 0, there is no linear relationship between the two. Keep in mind that correlation does not mean causation though.
This is the relationship between number of hits and team points:
Which is to say, there is no relationship. Things are all over the place. So why does this matter?
As far as I can tell, this contradicts the general perception about physical play among fans, who see aggressive play and hard hitting as things that good hockey teams do. An article on NHL.com said of the 2013-14 Blue Jackets, “[Coach Todd Richards] not only insisted the Blue Jackets play fast, get in on the forecheck and play responsibly, but he also wanted to play hard in every zone. That message was heard loud and clear. Columbus set a franchise record with more than 2,500 hits this season.”
Of course they’re good, they hit a lot of people! That League-leading number of hits resulted in 93 points and a trip to the playoffs. Do you know who was dead last in hits? Chicago, who had 107 points and advanced three more rounds in the post-season than Columbus, who were knocked out in the first round.
In this case the writer was not actually wrong in what he wrote (we’ll come back to that in a moment), but you can start to see the problem with thinking descriptive stats are predictive. An announcer or writer being wrong might not be a very big deal, but if a coach designs a strategy under the impression that it will result in better outcomes, he might not have a job for very long. As fans, the more we know about what has an impact on the game, the better we can analyze play and spend more time studying what matters.
What Actually Matters?
Let’s take a look at a few things you hear thrown around during hockey games like, “This team needs to get on the board first.” We have info on that, which tells us that teams who scored first won 68% of the time over the past three full seasons. Perhaps they do not need to score first, but there is clear evidence to suggest it is an advantage. Unfortunately, things are not always so clear.
Announcers often credit a team’s success to how well they perform on special teams. There are a few ways to say this and the phrasing makes a difference. The key factor here seems to be that teams who score more goals are more successful. Full stop. League-wide 20% of goals scored come with a man advantage, but whether a team puts 15% or 27% of their goals in the net while on the power play does not make a difference. As long as the puck ends up in the net, they are all worth one point. (Remember this before you make power play points a category in your fantasy league.)
When it comes to being down a man, there is no correlation between penalty minutes and team points or goals allowed. Rather than PIMs, we should pay attention to penalty kill percentage. Teams will kill anywhere from 75 to 90% of penalties against them, so a penalty will hurt the team with a bad PK team more than one with a good one. No matter how good you are the number of penalties you take will increase the number of short-handed goals you allow, but the teams who take the fewest penalties will not always have the best PK% either.
What about age? Are young legs more important than experience? No, it does not matter much.
Can you score more goals just by shooting more? With an R-squared of .59, shot percentage and number of goals scored are about as strongly correlated as anything else we have seen, other than goal differential (not that .59 is particularly high). But with an R-sqared of .11, the number of shots a team takes hardly has any connection to the number of goals they score. And even with that loose connection: On average, the more shots your team takes, the lower their shot percentage gets, not higher. The next time you are yelling “SHOOT!” at your television, remember, setting up a high-percentage shot is probably worth a few extra seconds.
On the other end of the spectrum, what about blocking shots? Surely that helps to decrease goals? Not really. Again, the relationship hardly exists, but surprisingly teams who block more shots actually allow more goals, on average. Announcers often praise blocking shots—and blocking a shot is better than not blocking it—but there are more alternatives to blocking the shot than letting it go through, like not allowing the other team the chance to get a shot off in the first place.
We Need to Watch to Understand the Stats
Things are not so cut and dry as we might want to believe, which can be tough to admit if you have been watching a sport for a few decades. Should we stop showing or even counting stats without predictive power? No way, descriptive stats add a completely different dimension to watching a hockey game. We just need to be aware of them in context; to know that more is not necessarily better. We should not let the stats distract us because they exist: We should not hit guys more because they count hits, we should hit them because it is part of our team’s strategy.
Can physical play help teams? Of course it can, but it is just as important to realize that success is possible without physical play (or with fewer blocked shots) as well. The Blue Jackets found success by hitting guys all over the place, the Blackhawks found it by doing just the opposite. There is more than one way to win; teams rarely need to do anything. Basketball coach Stan Van Gundy talked about the same situation in the NBA:
Everybody’s gotten into these generalizations that you need free throws, shots at the rim, and threes. That’s all well and good, but if you don’t have guys who can shoot the threes, that doesn’t help you a lot. The Celtics won the championship in 2008 and they took more mid- and long-range twos than anybody in the League and they shot them better than anybody in the League because that’s what they had as a team. It has to be part of an overall philosophy that fits your personnel…
Announcers often fall into the trap that Van Gundy pointed out and mislead viewers by oversimplifying the situation. If we, as fans, hear an announcer say, “This team should be doing X more,” we should figure out if X actually does have a connection to the team’s strategy. After all, it is the announcers who get to watch more hockey than anyone, which should allow them to find the numbers that are most relevant to a team’s playing style and pick up on when they are falling short of their game plan.