Are there unintended consequences to the coach’s challenge?

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On a Canucks broadcast earlier this season, Sportsnet’s John Garrett pointed out that we seem to be getting a lot more offside calls this year. And for once, I actually agreed with him.

Garrett theorized that maybe this was an unintended consequence of the coach’s challenge. Perhaps linesemen don’t want to be responsible for having a goal called back because they got the call wrong at the blue line. So if it’s a close call, just be conservative and whistle it down. Coaches can’t challenge an offside call, after all.

The NHL introduced a coach’s challenge to try and get more calls right. And clearly, it should be in everyone’s interest to do so. But what if we’re not just getting more calls right? What if we’re also getting more calls, period?

Ever since that broadcast, every game I’ve watched seems to be rife with offside calls on any play even remotely close at the blue line. It doesn’t matter the player, the team or the score. Bobble the puck? Offside. Drag the skate? Offside. Make an extra move? Offside.

At best this is slowing down the game, but could it also be contributing to the reduced scoring we’ve seen so far this season?

If so, this is an observation that both John Garrett and I picked up on just by watching the games. Maybe Brian Burke is right and hockey really is an eyeballs sport.

Let’s find out.

In order to help me dig into this a bit more. Micah McCurdy graciously pulled the data from the NHL’s play-by-play files for the last eight seasons and this is what it looks like:

Season Games Offside Calls Calls per game YTY Change
2007-08         1,230 6,498 5.3
2008-09         1,230 6,283 5.1 -3%
2009-10         1,230 6,234 5.1 -1%
2010-11         1,230 6,512 5.3 +4%
2011-12         1,230 6,637 5.4 +2%
2012-13           720 4,601 6.4 +18%
2013-14         1,230 6,400 5.2 -19%
2014-15         1,230 6,757 5.5 +6%
2015-16            225 1,622 7.2 +31%

With the exception of the lockout season, offside calls have in the past averaged between 5.1 and 5.5 per game. This year there have been 7.2 offside calls per game.

Clearly something is going on here. So score one for the eyeballs.

Through Tuesday’s games there have been 31% more offside calls this year compared to last season, which was already on the high end of the normal range. The average over those previous eight seasons, including the abnormally high lockout-shortened season, was 5.4 offside calls per game. So far this year we are seeing two additional calls per game.This might not seem like much, but it’s a 35% increase. That seems huge. But is it significant?

Other than the lockout season, the number of calls per game has stayed within a very narrow range. We’re well outside that range this year, so at first glance it appears to be more than just simply random noise.

offside calls

But what about that lockout year? There we have a shorter season and the number of offside calls per game is outside the expected range.

Is what we are seeing is simply a function of sample size? Maybe the game-to-game variance is high enough that even the unusually high number of calls so far is actually reasonable given we’re only about one-sixth of the way through the season.

Or perhaps early in the season the timing is off, both for the players and the linesmen. And as the season wears on, the number of calls comes down. That could explain the lockout data: the number of calls regressed only part way back down to the average because the shortened season ran out of runway.

And this is exactly what we find when we look at just the first 225 games of each season:

Season Offside Calls Calls per game YTY Change
2007-08 1,467 6.5
2008-09 1,497 6.7 +2%
2009-10 1,394 6.2 -7%
2010-11 1,487 6.6 +7%
2011-12 1,557 6.9 +5%
2012-13 1,425 6.3 -8%
2013-14 1,496 6.6 +5%
2014-15 1,608 7.1 +7%
2015-16 1,622 7.2 +1%

Sure enough, the number of calls is higher at the start of each season. Except, strangely enough. in the lockout season. Perhaps it was simply that players’ timing was off for most of that compressed season rather than just at the beginning, and so there was no regression back down to the 5.2-5.5 range. Either way, it is clear that what we have been seeing so far this year is not that far outside the ordinary. In fact, it is barely changed from last year, and only 9% above the average for the previous 8 seasons.

Since we are told that hockey is an eyeballs game, here’s the data in graphical format:

offside calls vs 225 games

The year-to-year trend over the first 225 games is slightly upward. We have been seeing gradually more calls overall, but it’s not a huge change. And it’s only when you compare the early season to an entire year that the change appears to be significant change.

So it’s not that your eyes are lying to you. They’re not. What you are seeing is real. It’s that your brain doesn’t remember that last year started pretty much the same way. And since it wasn’t in place last year, I think we can discount the theory that the coach’s challenge is somehow responsible for the observed uptick in offside calls.


One corollary to this analysis is that we can also look at how the gradual change in offside calls might be having an impact on the hot topic du jour: the perceived decrease in goal scoring.

But first let’s make sure this decrease in goal scoring isn’t just an early season phenomenon as well.

Goals per game 225 GP and season

And the answer is no.

In fact, up until the lockout-shortened season, goal scoring was typically higher in the first 225 games and then drifted down to finish about a tenth of a goal per game lower by the end of the season. So if anything, we should expect the current goal scoring rate to drop as the season wears on.

But before you rip up your season tickets and cancel your GCL subscription, you should note that in the post-lockout period this has not actually been the case. Instead, by the 225 game mark, the goal scoring rate is pretty much set for the rest of the year. So if this holds up, at least this season won’t get any worse.

That being said, all this talk about needing to do something about goal scoring is either four years too late or a tempest in a teapot. We have been right around 5.3 goals per game since 2011-12, and this year is really not that much different. (Mind you, I’m going to guess that the 3-on-3 overtime is helping to prop up that number.)

But justified or not, the perceived lack of goal scoring is currently a contentious issue, so let’s look at the relationship between offside calls and goal scoring over the first 225 games of each season:

Offside vs Goals 225 GP

Keeping in mind that correlation does not necessarily imply causation, but it is worth noting that approximately 40% of the decrease in goal scoring over the last  nine seasons coincides with an increase in offside calls.

But let’s be clear, it’s not the offside calls themselves that are resulting in lower goal scoring. The offside calls are simply an indicator or symptom of some other factor at play.

Nick Mercadante weighed in on this point with some practical advice for defensemen:

An increase in offside calls may be a function of better defense, which can frustrate the puck carrier into delay and disrupt the timing on the zone entry. Often those disjointed types of games aren’t all just offensive miscues and poor timing on the part of the attackers. It can be the result of a proactive defense stepping up to force decisions at the blue line.

This is one of the better methods at disrupting clean entries, and, in turn, transition offense. Thus more offside calls could signal better defense, which in turn is allowing fewer goals.

And indeed, this might provide an actionable lesson. One that is already taught in many systems, but should be reaffirmed nonetheless: forcing the issue at the blue line is generally a great idea and can be taken a step further. Stocking your defensive corps with players that can control the gap and aren’t afraid to step up because they have an elite turning capability (e.g. Stralman) can also really help to stop an offense before it gets started. At the blue line.

So while there are assuredly other factors at play, it certainly appears that zone entries and the ability to disrupt them could be partly responsible for both the slight increase in offside calls and the observed decrease in goal scoring. Keeping in mind that most of that decrease happened four years ago.

Thanks again to Micah McCurdy for help compiling the offside data and Nick Mercadante for the insight on defensemen disrupting attacks at the blue line. You can find me on Twitter at @petbugs13.

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