The Power of Puck Luck

“Puck luck” is real. And it’s powerful.

In early December, when Calgary was riding a white hot 17-7-1 start, we wrote an article explaining that its success was nothing but smoke and mirrors. We pointed out that puck luck was duping just about everybody from Toronto to Timbuktu into believing that the Flames were an up-and-coming contender, when in reality they’re Michael Spinks and most of the rest of the NHL is Mike Tyson. On cue, reality set in and Calgary promptly lost its next 8 games.

So what exactly is puck luck from a hockey analytics perspective?

In a nutshell, there are certain crucial aspects of performance that tend to vary significantly in the short or even medium term (say 10 to 40 games), but which virtually always return to long term averages. “Puck luck” is just shorthand for whether a player or team is running unsustainably hot or cold as compared to those long term averages.

The most important of these performance metrics are shooting percentage and save percentage. It’s not news to anybody that players often go on hot streaks where every time they touch the puck it seems to bulge the twine, or cold streaks where they couldn’t hit the ocean from the side of a dock. But what people seem not to always appreciate is that over time these streaks end and players almost always revert to their historical average shooting percentages.

There’s even a stat specifically designed to provide a very rough measure of puck luck: “PDO.” PDO is nothing more than a single number that adds a team’s shooting percentage and save percentage. By definition the league average PDO is exactly 100 (because save percentage is the inverse of shooting percentage). Teams with particularly skilled shooters or puckstoppers (or great team defense) can maintain a PDO of 101 or even higher, but as a rule of thumb any team with a PDO of above 101.5 (or below 98.5) is probably running unsustainably hot (or cold) and can expect the inescapable gravity of regression to historical averages to take hold and pull the team back down (or up) to its expected percentages.

The Buffalo Sabres have been kind enough to provide us with a textbook example of the power of puck luck. Over their first 18 games the Sabres won 3 and lost 15. They scored an almost impossibly low 9 goals in their first 10 games, including being shut out 4 times.

But in their next 13 games they won ten times and scored 44. Had the Sabres turned the corner? Had they instituted new systems that plugged the gaping holes in their defense while simultaneously jacking up their offense to the point where it was the most potent in the league? Had they secretly lured Wayne Gretzky out of retirement and covertly named him Zemgus Girgensons just to throw everyone off the scent?

Let me put it this way: all of the above are equally plausible explanations.

As the table illustrates, the Sabres’ 13 game hot streak was all about puck luck.

BUFFALO SABRES 2014-15 (5v5)

Games Corsi For % Corsi For /60 Corsi Against /60 Corsi +/- per game Sh% Sv% PDO
Games 1-18 37 (30th) 40.4 (30th) 68.8 (30th) -22.7 (30th) 5.9 (28th) 91.7 (17th) 97.6 (26th)
Games 19-31 38.7 (30th) 40.6 (30th) 64.4 (29th) -19.4 (30th) 10.5 (1st) 93.6 (5th) 104.1 (1st)



Other than a slight improvement in Corsi Against, the Sabres’ shot metrics during their 10-3 streak were virtually identical to their 3-13-2 start. But their save percentage jumped from 17th overall to 5th, and their shooting percentage almost doubled, rocketing the Sabres from 28th to 1st (stats courtesy of Several of the Sabres’ top scorers were shooting miles above their historical percentages. Marcus Foligno was shooting 27.3% (compared to his career average of 12.6%), Girgensons shot 26.7% (9.9% career average), Matt Moulson 19.2% (13.4% career average), and Brian Flynn 15.0% (8.7% career average).

Ironically, Buffalo’s puck “luck” might have been decidedly unlucky, since it’s only practical effect was to jeopardize Buffalo’s odds in the Connor McDavid sweepstakes.

If you’re a Buffalo fan you shouldn’t worry too much though, the hot streak was never sustainable. It wasn’t “real” in the sense that it was reflective of some actual improvement in the Sabres’ play, it was just puck luck at work. As demonstrated by the Sabres’ much more representative one win in their last nine games, your team is still by far the worst in the league and I promise it will be in the thick of the hunt for that first overall pick at season’s end.


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