What's Up With All These Penalty Calls?

This article on 538 annoyed me. It says scoring is up in the NHL this season, and basically points to more penalty calls being a key (if not the key) reason. The chart in the article shows that all minor penalties are up from 6.65 per game in 2016/17 to 7.09 per game so far in 2017/18. This a 0.44 increase - so about half-a-penalty per game, or a 7% increase. If you look closely at the chart, the increase is almost entirely due to the increase in slashing calls.

I complained on Twitter [is it redundant to say that?] about my issues with the article, but what really got me was the conclusion:

To be sure, no one in the league office of the NHL is losing sleep over this. More scoring is good news for a league that has been plagued by a spate of absurd calls from pundits to not only tweak the rules of the game, but to change the shape of it too. Reprimanding centers for lining up at the dots incorrectly? Fine, we can all live with that. But making the nets bigger? That’s downright sacrilege. Thanks to the relatively high-scoring climate of the present-day NHL, maybe we can put that tired argument to bed once and for all.

I am all for more scoring (and more importantly more scoring opportunities and flow), and I agree that more penalties being called is an important way to get that. But suggesting that the NHL has solved its scoring woes - and the "tired argument" about scoring can be "put to bed" - because penalties are up a fraction only a 1/3 of the way into the season seemed, to me, premature. [It was also probably unnecessarily snarky, but welcome to the internet I guess]. So I grabbed the 2017 penalties per game from Corsica [please donate!] to see if there may be any trend in how many penalties were being called as this season has progressed.


Corsica does not separate out minor and major penalties (or exclude offsetting penalties in team results) so this shows all penalties called in each game so far this season. I can't think of a reason to think that the rates of minor to major penalties changes over the course of a season, so I will assume we wouldn't see a difference using total penalties instead of only minor penalties. ESPN does have this data, so maybe that's a more granular project for another time. Note that I pulled only "home" games, and then added up penalties drawn and taken to get total penalties per game. Note also that for this chart (unlike the chart I originally posted ), I excluded Las Vegas.

So already this season, we are seeing a slow, downward trend in total penalties called. More penalties were called in the early season games than the more recent games. Maybe it is premature for 538 to suggest the NHL's Scoring Problems Are Solved. Or maybe my guess is wrong, and we'll see the number of penalties increase in the last 2/3 of the season? I wonder if that's ever happened before?

The following shows trends in total penalties called per game for each full season in the BehindTheNet era (2007 to current, ignoring the 2013 lockout season). Note also that I set each y-axis to a max of 35, so that we could compare the trends accurately year to year. This of course cuts off a few brawl games where penalties exceed the norm, but that doesn't affect the trend lines. 

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In no season did total penalty calls appear to increase as a season progresses. 2007/08 and 2015/16 are basically flat, and the others show some downward slope. In 2007/8 and 2008/9, calls start above the 10 per game line, and then seems to drop a little bit each season. That makes sense, since we know that prior to this season, power-plays per game have been steadily dropping for years. So even though penalties may be up compared to last season - we still might not be reaching levels called even 4 seasons ago. We can see the trend when the entire time frame is graphed (the blue line estimates the start of the 2017/18 season).

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Now maybe 2017/18 will be the year that "reverses" the downward slope as the season goes on. Maybe the NHL is watching overall penalty calls/PP chances and will reinforce with officials the need to call more penalties to keep scoring levels up. Or maybe 538 was a little premature in saying the NHL scoring issues are resolved and in assuming that "more" penalties will continue to be called the rest of the season.

...Again I'm right in my analysis.