## Mulling over defence vs offence in advanced statistics

Sometimes my brain leads me into some strange places. Other times, it asks incredibly mundane questions, such as is it better to score goals or prevent goals? To win games, you obviously need to do both, which is why the question sounds dumb. But it’s a fundamental part of team philosophy. The cliché is that “defence wins championships” and even if defence and offence are nearly equal in determining success, that “nearly” can make all the difference.

In this case, that dumb question led me to spend a whole bunch of time poring over numbers, creating graphs, and pondering how defence is handled by the current advanced statistics we have available. I probably should have left well enough alone.

Now, I am not much of a statistician. I stopped studying math after 1st-year calculus, but I understand the broad strokes. For this, I just wanted to do some quick and dirty statistical analysis. I just wanted to figure out whether goals for or goals against correlates more strongly with winning.

So I took the last 5 NHL seasons and all 30 teams and took a look at their goals for and against. I stuck with 5-on-5 and took out empty net goals to keep things relatively even for all the teams. I then charted those totals against each team’s wins each season. Here is the result:

When I saw these two graphs, I have to admit to being surprised. It’s not just that allowing fewer goals correlated with winning more strongly than scoring goals, it’s the degree to which it is the case. It appears that preventing goals correlates far more strongly with winning. Now, I may be mistaken, and someone more knowledgeable in the area of statistics may come in and explain that the correlation I’m seeing here isn’t statistically significant, but it looks fairly significant to me.

19 teams reached 50 or more wins in the last 5 seasons. 8 of those teams scored fewer than 160 goals at 5-on-5. Only one team, the 2011 Pittsburgh Penguins, allowed more than 160 goals at 5-on-5. In general, a far surer path to victory is paved with solid defence, while teams can do far more than get by with a mediocre offence. The 2006 Dallas Stars got to 50 wins with just 122 goals at 5-on-5. Even the 2009 Washington Capitals, who had the most 5-on-5 goals for in the last 5 seasons with 213, only allowed 136.

Now, this isn’t anything ground-breaking, but it got me thinking about how defence is usually treated in advanced statistics.

The big two most referenced advance statistics, Corsi and Fenwick, are built around the idea of puck possession. They’re founded on the basic principle that getting more shots on the opposition net is better than allowing more shots on your own net, which seems pretty sounds.

In some ways, proponents of puck possession would advocate that the best defence is a good offence. A defensive tactic like blocking shots is downplayed in importance, as blocking a shot means something has already gone wrong: the opponent is shooting the puck. Cam Charron once paraphrased General Patton regarding shot blocks: “No bastard ever won a game by blocking shots. He won it by making the other poor dumb bastard block his shots.”

As long as the puck is in the offensive zone, no trouble will come to the defensive side of the ice.

This is all well and good, but it feels like something is missing. It strikes me that the advanced statistics we currently have available do not have a particularly good grasp on goal prevention. The general tactic seems to be to wrap it up with puck possession as part of a package and use Corsi or Fenwick as a catch-all for both offense and defence. But if preventing goals does have a stronger correlation with winning than scoring goals, it seems like that should be taken into account.

Defencemen seem to get short shrift, to the point that Vic Ferrari, creator of the essential timeonice.com, was quoted as saying, “It becomes obvious very quickly that forwards are driving the outchancing-at-evens bus … defensemen are just riding it.” Poor defencemen.

But if the focus is on outchancing the opposition and possessing the puck, this is likely true. But the role of the defenceman is, mostly, to ensure that the results of the opponents’ chances and possession are foiled rather than creating chances and puck possession for their own team. How do we take measure how well a defenceman performs in that role if something like Corsi doesn’t capture it accurately?

One of the other problems is that there aren’t many advanced statistics that take goaltending into account. While even-strength save percentage, the various “quality start” metrics, and GVT are useful for evaluating goaltenders, there doesn’t seem to be anything that integrates a teams quality of goaltending with overall team performance. Advanced statistics also don’t seem to have much of a handle on shutdown defencemen, beyond pointing back to Corsi and Fenwick.

This isn’t meant to be a criticism of advanced statistics; I’m just honestly curious how these problems can be solved or, if a solution already exists, I want to know about it. It just seems that, right now, the advanced statistics community is focussed so much on what pushes possession forward that it might miss what prevents the opposition from doing the same. It might seem like they are one and the same, but preventing goals appears to be more important than scoring them when it comes to winning.