Monday, February 05, 2007

How much of home field advantage is the officiating?

There are many factors that could cause home field advantage (HFA): refereeing, travel, park familiarity, crowd support, and many more. And there have been studies that have checked some of these. In “The Diamond Appraised,” for instance, Craig Wright found no effect for crowd size, and that teams playing in brand new parks had only slightly below-average HFAs. But, when the new park was in the same home city, the HFA was actually higher than average – it was brought down by lower-than-average HFAs for the new-city parks.

Wright also found a huge HFA for triples – he advanced the theory that players at home know exactly how to play balls hit off the wall to limit opposing hitters to two bases.

I just ran across this
recent NBA study on home field advantage by Roland Beech. What that study suggests to me is that refereeing plays a significant role.

The study compared NBA home and road statistics in several different categories. The home team was superior in every category – with one exception: free throw percentage. Here are some of the results:

............ Home ... Road

FG% ........ .460 ... .447
Off. Reb. %. 30.6 ... 28.5
Def. Reb. %. 71.5 ... 69.4
FTA ........ 27.0 ... 25.6
FT% ........ .746 ... .744

Where does the refereeing come in? Well, free throw percentage is the one category in basketball where there’s no possible influence from the referees. And in that one category, home teams had almost exactly the same performance as road teams.

That’s not what I expected to see. I would have expected a modest improvement in every category across the board. If players are just physically and mentally not at their prime when on the road, that should affect free throws too. But there was hardly any difference there.

With regard to foul calling, Beech notes that the the free-throw HFA accounted for 1.3 points per game. The overall HFA was 3.4 points per game. Still, that’s pretty significant, 38% of the total. You’d have to acknowledge, though, that not all of that difference – in fact, not any of it -- need be referee bias. It could just be that road players commit more infractions than home players. But still, the difference is suggestive.

And all the other categories could also be significantly influenced by referees. If road players know they are more likely to be called for a foul, they will play less agressively. And so even in cases where a foul isn’t called, their stats should be lower, both on offense and defense.

Similar research for baseball can be found in
this study from Tom Meagher (previously mentioned in this blog in the comments here). Meagher found that most of the HFA can be explained by walks and strikeouts. In fact, if home and road teams were equal in every category except K and BB, the home team would have a winning percentage of about .520. Since the actual HFA is only about .532, we can see that balls and strikes form a very large proportion of total home field advantage. And, of course, balls and strikes are the category in which umpire judgement figures most prominently.

And, as in basketball, the other categories would also be influenced by umpires. A pitcher on the road who notices a shrunken strike zone will get behind in the count and have to give batters better pitches to hit. This could account for the fact that there is still some HFA in the results of ground balls put into play – the umpire effect would mean home batters hit “better” ground balls off worse pitches.

Following this line of thinking, it’s even theoretically possible that *all* of the home field advantage could be attributed to refereeing. I don’t think that’s the case – I believe that other factors exist (Wright’s explanation of the triples effect, for instance, seems right to me). But I do wonder if refereeing is a bigger effect than originally thought.

How would you find out? I’m not sure you can. But you can start by finding categories where, as for free-throw percentage, refereeing should have little or no effect. You could look at NFL field goal conversions, or the results of NHL shootouts. If every such category shows no advantage to the home team, that would reinforce the theory that HFA is predominantly refereeing.

And you can also look at sports where refereeing isn’t a factor at all – golf or tennis, say, or bowling. The HFA in those sports could give a strong suggestion of how much of the advantage in other sports is inherent in the players’ performances. Anything above that amount, in refereed sports, we’d suspect is a function of the officiating.

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At Monday, February 05, 2007 10:42:00 AM, Anonymous Anonymous said...

I don't know a lot about basketball, but I do know that teams tend to commit more fouls when they are behind late in the game. So the FTA difference could be as much a result as a cause of visitors' losing. I think you would need to do something like look at first-half fouls, or fouls in wins and fouls in losses separately, to sort this out.

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You seem to be assuming that the cause of HFA, especially the role of officiating, will be the same in various sports. But I don't see why that needs to be true. I would think that the emotional/motivational impact of home crowd support could matter more in NBA than MLB, for example, both because of crowd proximity and because it's a contact sport. It seems to me that dominating your opponent on the boards is just a very different activity than hitting a baseball, in terms of the value of emotional intensity (it probably helps in rebounding, might even hurt in hitting). In the same vein, I would say FT% is not unique only in terms of the non-impact of referees, but also it's the one thing in basketball where (like hitting) you may want serenity more than intensity.

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For some reason, it always takes me 2 attempts to post here. Any way you can lighten the security?

At Monday, February 05, 2007 11:55:00 AM, Blogger Phil Birnbaum said...


Absolutely right about fouls late in the game, I should have thought of that.

Also agree about differences in different sports; your point about intensity makes sense. But many of the theories of HFA should apply roughly equally to different sports -- travel, familiarity, nutrition, etc. I'd bet they are more alike than different, your valid example notwithstanding. But I could be wrong.

I don't think I can change the security except to get rid of the verification, and when there was no verification there was a lot of spam. Sorry! Unless anyone else knows of a solution.

At Monday, February 05, 2007 12:35:00 PM, Blogger Tangotiger said...

Regarding the travel: I think this is an issue. I seem to remember looking at this in the NHL, and we have cases where the travel is exactly the same: playoffs. And I think the home ice advantage is less in the playoffs.

(You'd have to be more careful, because of Game 7 of one series to Game 1 of the next might be in the same city, but then their opponent might have been well-rested. In any case, you can focus just on the first series.)

Plenty of data for someone to work with.

At Monday, February 05, 2007 8:54:00 PM, Blogger JavaGeek said...

Hockey it's actually easy to see the officiating effect.

It’s interesting to note that there are an additional 405 penalties given (only minors) to the away team (1/3 per game) (8199 vs. 7794), might sound like a little, but this should work out to around 60 goals. If you just look at the more subjective calls (the ones they can ignore) you get a more significant difference of 390 (6457 vs. 6067), which is a lot larger as a percentage. Interestingly these power plays resulted in 1382 power plays goals for home and 1162 for the away team (difference of 220), which suggests this problem is a little more complicated. A way a referee can get the home team more goals without giving more penalties is to give them a little closer together so as to result in “5 on 3”s. The home team scored 266 “5 on 3” goals vs. 189 “5 on 3” goals for the away team. ... either way the home team is getting a lot more “5 on 3”s (or scoring with them at much high rate).

The total difference in one season for home vs. away around 400 goals. Based on this information officiating can account for nearly half of the goals. There are other ways to help the home team in hockey as well, such as: disallowed goals and quick whistles.

At Thursday, February 08, 2007 9:21:00 AM, Anonymous Anonymous said...

The free throw effect may have an alternate explanation other than it is official-neutral. You could argue that free-throws are the only stat mentioned where aggressiveness and strength are not positive factors in the result.

I remember hearing of a study where british soccer players were asked to provide spit samples just before a match - and the testosterone levels were higher in the home team spit. So maybe evolution has developed us to defend the home by way of extra physical aggression (which helps rebounding and drawing fouls, but not shooting FT).

At Thursday, February 08, 2007 9:39:00 AM, Blogger Phil Birnbaum said...

Now THAT would be cool, if the home field advantage was the result of evolutionary forces that make people more agressive defending their home turf!

Is there any test for that theory, any other obvious situation in sports where aggressiveness isn't an asset?

At Friday, February 09, 2007 7:11:00 PM, Blogger TBW said...

Home advantage is a topic that has been studied quite a bit in academic circles. I'm not familiar with all of the research, but I have a copy of a 1992 literature review by Courneya and Carron from the Journal of Sport & Exercise Psychology.

Regarding basketball officiating, the article cites a 1987 study by Lehman and Riefman in the Journal of Social Psychology that found that "significantly fewer fouls were called on star players at home than away; no differences were found for nonstars." Their data were limited to Lakers games from the 1984-1985 season, so it's hardly a definitive result, but it does suggest one specific factor behind the home team's statistical superiority.

At Friday, February 09, 2007 10:17:00 PM, Blogger TBW said...

The 1992 Courneya and Carron article I mentioned in my previous comment was updated by Carron et al. in the April 2005 issue of the Journal of Sports Sciences -- incidentally, that issue's articles are all related to the home advantage in sports.

On the topic of officiating bias, the latest review cites a study by Nevill, Balmer and Williams in 2002 (Psychology of Sport and Exercise) that isolated crowd noise as a significant influence on officials' calling fewer fouls against the home team in soccer. Here's a recap of that study by Carron et al.:

"Nevill, Balmer and Williams (2002) examined whether the presence or absence of crowd noise influenced officiating assessments of the legality of 47 challenges/incidents during a recorded English Premier League match between Liverpool (home) and Leicester City (away). The officials (n = 40) were exposed to either an audible crowd noise group (i.e. the match was shown with audible crowd noise) or a silent condition group. The results showed that the officials in the audible crowd noise group called significantly fewer fouls against the home team than referees in the silent group condition. Furthermore, the decisions made by the referees in the audible crowd noise group were in close agreement with those of the match referee. However, it is interesting to note that officials in both conditions did not penalize the away team more often. Taken together, the results indicated that the presence of crowd noise reduces the number of fouls awarded against the home team rather than increasing the number of infractions called against the visiting team."

It's not much of a stretch to also attribute crowd noise to the foul discrepancy in basketball.

At Friday, February 09, 2007 10:21:00 PM, Blogger Phil Birnbaum said...

Thanks, Drew. I have the Carron/Loughhead/Bray article downloaded, but couldn't get the Courneya/Carron one.

The Carron et al article mentions that 75% of opening day MLB games are won by the home team. Could that be right? I can't find the the paper (by Ward, I think) that's referenced.

At Saturday, February 10, 2007 4:05:00 AM, Blogger TBW said...

75% does seem rather high. I don't have access to Ward's article either, so I don't know if there was anything unusual about his methodology. I suppose one could confirm that number using Retrosheet data.

At Thursday, February 15, 2007 10:04:00 AM, Anonymous Anonymous said...

Phil, on your question of testing for evolutionary agressiveness, i believe there are many examples in natural science journals of animals exhibiting this behavior. Off the top of my head, a "home spider" would beat an "away spider" > 50% of time for web territory even if the home spider was smaller. How to translate into games, I'm not so sure.

But with respect to differentiating out official bias vs aggressiveness bias, you are right you could look at sports with little aggressiveness involved (archery, bowling?) but you could also look at sports where little officiating is involved (track and field, wrestling?)

At Thursday, February 15, 2007 11:01:00 AM, Blogger Phil Birnbaum said...

That is very, very interesting ... Thanks, Nate! Do you happen to recall if those papers gave any ideas *how* the home spider defeated the stronger visiting spider? Knowledge of how to use the web? Just greater strength and agility than normal? More aggressiveness?

At Thursday, February 15, 2007 3:21:00 PM, Anonymous Anonymous said...

I don't recall anything specific about how the spiders won (phychological, physical, or inside knowledge) - but the argument for why was from the field of evolutionary game thoery: that a society composed of individuals at 103% strength defending home and 97% strength attacking away would be better off in the long run because fights would be less common.

Of course in sports, you have to fight. But the predisposition is still there.

A book with some nature examples is: Evolution and the Theory of Games by John Maynard Smith. It is very dense and occasionally dry though...

At Saturday, February 17, 2007 11:09:00 AM, Anonymous Anonymous said...

Here's a nice paper on home field advantage written by Michael Lerra of the HireMeTheo blog. It includes a pretty good survey of the existing academic research on the subject.

What amazes me is that the home advantage has been observed so univerally across sports, across levels, across eras, across continents, yet there is still little consensus on the exact factors that contribute to its effects. But both officiating bias and aggressiveness are intriguing ideas that probably haven't been examined as thoroughly.


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