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post Book Report – Why NHL Teams Win at Home

February 26th, 2011, 7:39 pm

Filed under: blog — Written by Mike

I like reading sports books, and I like reading economics-type books.  Which is why I was interested to read Sportscasting: The Hidden Influences Behind How Sports Are Played and Games Are Won.  Worst case, they’d have some interesting theories about sports with scarce or anecdotal data to back it up (the way some people criticize Malcom Gladwell’s work) and best case it would really shed light on some interesting sports conundrums.  So which is it?

Actually, the latter.  And in order to achieve it, the authors crunched a ton (is it tonne in Canada?) of data.  It’s not nearly as breezy as a Gladwell read, but it’s meatier.  More tables, more numbers, more statistics, more explanations and hedges about what can properly be controlled for, and what can’t.  Those who have read this site for a while and listened to our podcasts know I love that kind of thing.   A couple of long chapters of the book are setting up the dominos to answer the question- why do home teams have such a big advantage?

There’s no doubt there IS an advantage, and it’s substantial in pretty much every sport.  Soccer is the most lopsided, with well over 60% of games being won by the home team (they calculated the numbers for MLS, EPL, Serie A, La Liga, and others).  Basketball is next, with the NBA home teams winning 62.7% (they even calculate WNBA and college).  The NHL is next, with 59% percent of home teams winning, and football (57.8%) and baseball (54.1%) bringing up the rear.

So, some things that are interesting about this discussion, the first being obvious, the others not (but backed up by the data).

  1. Home teams win the majority of games, sometimes a significant majority.
  2. This winning percentage is constant across time.  The winning percentage of home teams was about the same 50 years ago as it was 10 years ago, or now.
  3. The winning percentage is directly related to the sport itself.  Japanese baseball home teams have about the same winning percentage as MLB home teams.  Arena football the same as the NFL.

I’ve never thought about this too much before, but even #1 is really remarkable.  Why do home teams win so much, and so consistently?  There has been no NHL season where away teams won more games than home teams. As watchers of plenty of NHL games, I’m sure we all think of several reasons why this is.  One is the home crowds- the home players play better when you’re cheering them rather than booing them.  Another is travel- away teams have to deal with hotels, unfamiliar surroundings, and jetlag.

Incredibly, the authors make very good cases that both of these are myths.  It’s really hard to control for home crowds, because there are so many other interactions going on.  But here’s one feat in hockey that’s essentially isolated from all those player and referee interactions- the shootout.  It’s basically an interaction between two players and the crowd.  So if the crowd were a factor in home player’s effort and performance, you expect the shootout to have a home-rink advantage the way the rest of the game does, right?  Well, it doesn’t.  Since the shootout started, away teams won the shootout 50.6% of the time.  The home-rink advantage just doesn’t exist in the shootout.

And, amazing, they manage to control for travel as well.  How could you do that? Well, what about teams that are really close together, like the Devils, Rangers, and Islanders?  You’d expect less home advantage when those teams play each other, because they don’t have to really go anywhere- just drive a bit further.  But if you look at those games, the home advantage is exactly the same as all the other games.  They found there is a small effect with back-to-back games, which in most sports occur more often on the road.  But that’s not nearly enough to explain it all.

So what the hell is it?  I’m going to put a break here in the post, because some people might actually want to read the book and not get the spoiler.  I’ve condensed many pages into this post, and believe me, it’s worthwhile to read all the other support the authors have come up with.  Or, more likely, you just want to bail out because there’s too many words reading sux zzzzz…..

It’s the refs.

The refs are biased towards the home team.  It turns out that the crowd really does matter, but not in the way you’d expect.  The screaming, unwashed masses don’t make Logan Couture play that much better, but they do, say, influence Bill McCreary not to give Detroit an extra 4-minute penalty when Logan Couture gets bloodied for the second time in a period.

This is a hell of an accusation, and the authors are fully aware of it.  They pull out the big guns, and really work impressively hard to make the case.  The biggest way the refs affect the outcome of the game is to call more penalties against the road team.  Home teams get 20% fewer penalties called on them than the away team, and given the average power play success rate (around 20%) that translates into about a quarter of a goal per game.  The average goal differential between home and away teams is 0.30 goals, so this accounts for almost all of the NHL’s home-rink advantage.

But couldn’t this bias be because of away teams playing worse, more sloppy, etc?  A compelling argument is made that this isn’t what’s happening.  The ambiguous calls- hooking, holding, tripping, etc. have a consistent and pronounced home bias.  If the away team was sloppy, we would also expect the same from less ambiguous calls, like delay of game (puck in the stands) too many men, and the instigator.

There is no home bias with these penalties.

And remember that the away team have actually won a slight majority of the shootouts since it begun.  If the away team was tired and playing poorly, wouldn’t you expect this to affect shootout results as well?  The ref plays almost zero role in the shootout.  It’s not a coincidence.

So assuming you buy this (and I do) the next question is why do refs call the games this way, all games?  And the answer is disappointingly simple.

They’re only human.

Psychologists have long documented the power of social influence.  This means the individual’s opinion of something will be influenced by the individual’s surrounding social group, and without the individual being aware of it.  The ref’s aren’t trying to get the home teams to win (although this does help the teams sell more tickets).  They are simply under pressure by a large crowd of people wanting things to go a certain way, and subconsciously, the refs make it happen.   One thing that supports this theory is that the larger the crowd is, the larger the home advantage.  This certainly stands to common sense- if 10,000 people influence the ref, 100,000 will influence them more.

What if I told you that the few soccer games that have been held in empty stadiums (due to out-of-control crowds) have no home-team advantage?

Anyway, this whole thing kind of tripped me out, and I thought it might interest you all as well.  As I said before, I’ve really simplified the arguments and left out essentially all of the supporting data, but it’s worth a read.  Sportscasting has lots of other discussions on similarly interesting topics.  I’d pick it up.

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    8 Comments to “Book Report – Why NHL Teams Win at Home”

    1. Tom says:

      I doubt think there is any way to track this but I’ve always felt teams having to play LA and ANA twice in a few days, then coming into SJ late because of our airport curfew, has had a major impact on visiting teams coming to HP. We tend to be the last stop on a west coast swing for many teams.

      Also, if NHL players agree that HP is one if the toughest and most hostile arenas to come into as a visiting team, then I have to think that has an affect as well beyond it’s affect on refs. The players basically admit it affects them too. I couldn’t imagine trying to perform under those circumstances…

      It is a very interesting topic. One that I’ve though about from time to time too, ever since the Sharks went a whole calendar year without losing in regulation….! It still boggles my mind…

      Anyways, just my two cents.

    2. Patrick says:

      There are tangible, game-related advantages to being the home team.

      NFL – crowd noisemakes it much harder for visiting offenses to communicate and work effectively.
      MLB – home team gets the last at-bat; each park is very different so familiarity is valuable.
      NHL – home team gets last change; home team has the edge on face-offs.

      I can’t really think of anything in the NBA, which is interesting because I’ve also noticed that home teams win so much more often.

      Anyway, none of the above is probably the book’s conclusion. I’ll take a guess and say it’s a matter of officiating… which also explains why the shootout results revert back to 50/50.

    3. Jason Veers says:

      This is amazing. I believe it. Thanks for an articulate and insightful post.

    4. Ruben says:

      I could have sworn I read something similar about the strike zone in baseball. This is really interesting stuff, which is amazing considering how obvious it is. If our US Supreme Court justices can’t prevent their biases from influencing their decisions (Bush v. Gore is an incredible display of each side abandoning their usual principles to vote for their choice), I don’t see how we can place much fault on officials for doing the same.

      Thing is, there really isn’t much of a solution unless you take the officials out of the arena. In baseball you can replace balls/strikes with computers (they already have Pitch/FX which tracks pitch locations), football is stop/start and thus you can review plays by video without affecting flow too much, but I just don’t see how it is possible to counter the issue in hockey.

      • Mike says:

        Ruben,

        The authors rely heavily on pitch/fx data for their baseball arguments. The strike zone does expand and contract to bias the home team, but also in other cases. You’ll have to pick up the book to read about what those other cases are.

        And maybe I’m just being naive here, but I can’t help thinking that one of the best ways to change behavior is to be aware of it. Does anyone else think that the officials are cognizant of these home biases, and try to counteract them? Neither do I.

        • Patrick says:

          Totally agree. It would have to come from the top, though, and you would never hear a league admit or draw attention to the fact that its officials are making systematically biased decisions.

    5. evilducks says:

      The solution:

      Deaf Refs.

      Hey, it’d be an interesting experiment.

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