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Wednesday, June 29, 2011

Home-ground advantage in sport: Theories

Home-ground advantage - theories and stats, Part 1

***Click here to see Ross of The Science of Sport talk you through home ground advantage in three video presentations, covering the theory and the stats.***

This past week in South African sport was punctuated by, among other things, a discussion around travel and the effect it has on professional sports teams.  The specific subject was the Sharks, a professional rugby team from South Africa, who flew to New Zealand for a playoff match in the Super 15 Rugby competition.  That discussion has turned out to be a nice catalyst for a couple of posts on home-ground advantage and the factors driving it (Part 1), followed by a post by Tuesday on travel and some interesting stats on how Super Rugby is influenced by both factors (Part 2).

Super 15 - an extreme model to study home-ground advantage

The Super 15, for those not in the rugby loop, is a tournament played between professional teams from South Africa, New Zealand and Australia.  It is now two weeks from its conclusion and is into the playoff phase.  The vast distances that are required, as well as the altitude for some teams in South Africa, make it a really great model to study home-ground advantage.  In fact, I'd go so far as to say it's unique in this regard, in that it has extreme travel (10 time zones a trip) and large changes in altitude (0m to 1600m) on a weekly basis.  But more on that next time...

Of course, travel is only part of the home-ground debate, but for the Sharks, it was the big one - they decided to leave South Africa on Tuesday, four days before the match, and so arrived, 10 time zones to the east, with only 2 days before a huge match.  The question then was whether it would be possible for the players to recover and perform optimally?

I thought it was pretty certain that they would not, which I said in the article.  Turns out they lost, 36 - 8, which is a pretty heavy defeat at this stage in the competition when you consider it's between the best of the remaining teams in the playoffs (3rd vs 6th in this case).

Of course, it would be an enormous oversimplification to say that the loss was due to travel fatigue, because sport is way too complex to reduce to one variable.  However, I think it probably played a part, particularly at the end of a long season and after some very physically demanding matches in the weeks before.

What wasn't quoted in the article was that I was of the opinion that the match would be very competitive for the first 30 to 40 minutes and then the scoreline would blow out.  The Sharks probably needed to be 10 points ahead with 20 minutes to play, because fatigue would influence performance more later, whereas motivation would "hide" it for a while, before it eventually told.  That fits with what eventually happened - it was competitive half-way, and the big defeat was inflicted in the second half.

Zero from 32 - the challenge of travel in Super Rugby at the end of the tournament

How big is home-ground advantage in the Super Rugby competition?  Well, consider that since 2000, not a single team has won a playoff match outside its own country.  That's 11 years, and thirty-two matches (they have playoffs and semi-finals), and not once has an international away team won.  Admittedly, part of this is because the home team is at home precisely because in the course of the season it has been better than the visiting team, but still, zero from 32 in a competitive tournament is a telling stat for how difficult it is to travel overseas in the final few weeks of a four-month long tournament.  

The main reason for that, I'm convinced, is travel, but I'll talk about travel in the context of Super rugby in Part 2 later this week.  First, let's look briefly at the science of home-ground advantage.

Home-ground advantage - consistently 50 to 70%

There is no question that home-ground advantage exists.  This article presents some numbers from US-sports, saying that in basketball, the home team wins 62% of matches.  In baseball and ice-hockey, 53%, and in the NFL, anything between 54 and 64%.  There is some evidence in football (that is, soccer, to avoid confusion!) that playing at home is worth 0.4 goals (1.5 vs 1.1 goal to home and away team over 5,000 analyzed matches).

For rugby, it's never been published, but I have done an analysis of the last five years of Super Rugby competitions (the format and number of teams changes every few years, so it's a shorter period) and in Super Rugby, the home team has won 61% of the matches they play.  If you break this down further into away matches against "national" teams compared to away matches internationally (ie: NZ side playing an SA/AUS side), then the figure is close to 80%, which is enormous.

You see the same thing, equally strikingly, when countries host international sports events like the FIFA Football World Cup or Olympic Games.  Medal hauls almost always increase at home.  There is a little more to this than simply competing at home, because the host nation almost always injects massive capital (human and financial) to improve sports performance, which is possible because countries know many years in advance that they are going to host.  So Olympic hosts perform better, but it may be due to increased spending to prepare athletes, in addition to the factors I'll discuss below.

Factors influencing home-ground advantage

This is a somewhat simplified summary of what we know, but generally, there are four factors influencing home ground advantage:
  1. Travel fatigue for visiting teams
  2. Familiarity with the city, the facilities, the playing arena
  3. Crowd factors, which can be further broken down into:
    1. How the crowd influence the players
    2. How the crowd influence the referee/officials
As mentioned, I'll tackle travel tomorrow, when I talk about Super Rugby, so let's look at the others, in reverse order.

The crowd influence on officials - a subconscious bias

Starting with the referees (a favorite of sports fans everywhere!), there is a real perception, true or not, that visiting teams are often ‘robbed’ by referee decisions. It turns out this is not a perception without some merit.  Studies have found, for example, that visiting teams in ice-hockey and basketball concede more penalties and have more players sent off for foul play than the home team.

It's also been found that the discrepancy in penalties awarded to visiting and home teams increases as the crowd increases in size.  And that when two London teams play football against each other, thus reducing the "unevenness" of crowd support, the discrepancy is reduced, suggesting that this may be the influence of the crowd on the referee. Even the most neutral and professional referee, with no intention of cheating can be swayed by the cheers or boos of a crowd.

For example, one study had football referees make judgments based on video footage of obvious foul play, but some refs watched without sound, while others watched with full sound, including crowd reactions to fouls. It turns out that with the sound, the referee is more likely to be swayed towards what the crowd is calling for - fewer free-kicks to away teams, more to home teams, no foul when the home team is guilty.  This is summarized in the figure below. And this is just on a TV screen, away from the cauldron of pressure of real-time action, where the crowd may have even more influence.

Further supporting this idea is that in the Olympic Games, the host country often wins significantly more medals, but most of them come in the subjectively scored events (ice-skating, gymnastics etc).  Given the football referee study, it's not difficult to see how a rapturous cheering crowd might be worth half a point here and there to a judge, despite their best efforts to block out crowd factors!

I must point out that there is other possible reasons why visiting teams are penalized more. One is that the "hostile environment" of the away arena produces a “victim” or “us against the world” attitude that sees visiting teams play more aggressively than they would otherwise.  This has in fact been documented for visiting teams, and, on occasion, for home teams, depending on the context of the match and the crowd behavior.

Also, the home team is often more aggressive and dominates play (defending their territory, perhaps), forcing the opposition to concede penalties as a result of applied pressure.  One analysis of decisions in the NHL found no difference in mistakes between home and away teams, suggesting that the penalty discrepancy may be justified (I am not quite sure how to reconcile that with the football study above, where the refs were making different judgments of fouls simply because of sound...)

Crowd influence on players - motivation, desire and anxiety

Harder to measure, but possibly as significant, is the effect of crowd support on player motivation and effort.  Certainly, sport is filled with testimonies of players who find "something extra", who raise their level because they're at home.  I guess one needs to be careful about taking a collection of testimonies and saying they are evidence (the plural of anecdote is not evidence!), especially because linking these factors to performance is very difficult.

But there's no question that "psychology" (an incredibly broad term) plays a role in sports performance.  But the sword may cut both ways when it comes to home-ground advantage.  A visiting team, with the odds against them, may well perform better than at home because of the desire to silence the crowd, and because of the added prestige of beating a team in their own country - I've experienced this with the SA Sevens side.

On the other hand, the effect of the crowd and the momentum they may give to players (who, for all the talk of "zoning the crowd out" must surely be aware of it) may be decisive - I have also experienced this with the Sevens team.  If you were to define a set of psychological requirements for success, you'd almost certainly put "confidence", "self-belief" and "high level of motivation" on the list, and in theory, that's what being at home brings.

To throw a curveball at that oversimplification of the theory, there was a fascinating opportunistic study a few years ago when a college basketball team had to play 11 of their matches behind closed doors because of a measles outbreak that forced the school to be quarantined.  It turned out that the team played better WITHOUT fans!  Their stats were up - more points, more free-throws and better shooting percentages.  Of course, 11 matches is a small sample when you consider how many factors might influence each performance outcome, but it does suggest that perhaps, fans influence players negatively, through increased anxiety.  Maybe the other team is just more anxious, and plays relatively worse!

Familiarity - 'no place like home'

The fourth and final factor, which is linked to the psychological factors I mentioned above, is familiarity with the playing venue, the weather, the training facilities, and also the people who the player encounters in the week leading up to matches.  There's some evidence for this too.

For example, in 37 sports teams who moved to a new stadium, home ground advantage fell by 25% in the first season at a new home (this is a small sample set, it must be noted, given the complexity of sports performance). The advantage still exists, but they are thus less likely to win at home than before.  Over time, this advantage returns.

Two things are in play here. First, they are no longer as familiar with their own stadium, and as trivial as it may sound, I believe this is a crucial aspect to performance, because it influences routine, focus, relaxation, confidence, and expectation prior to matches.  There may even be a more "primal" factor, in that the home team is protecting its territory, a theory that coaches play up all the time - the "our house" speech you may have heard a variant of!  New stadium, less territorial, less advantage?  Perhaps.

The second factor is that the visiting teams no longer have a potential psychological hurdle of entering the “fortress” that may have existed before.  This introduces the other side of the debate - the mindset of the visiting team.  In South Africa, we have a couple of rugby venues that are hostile to visiting teams, and knowing a few players, they don't particularly enjoy going there!  The media tend to hype up the fortress idea, and while players should in theory be able to resist this kind of intimidation, there's no question that mindset may be changed by the awareness of an away team.

In my experience, I actually feel that sometimes it is played up too much within teams.  Coaches and players always tell the media that it's still a game between two teams, a ball and four white lines, but they often create confusing internal messages, trying to downplay the mental aspect while simultaneously trying to inspire players to "be ready for the onslaught from the home team".  If any of this impacts the player, then home-ground advantage may have an effect through negative influences on the visitors.

Then there are also very specific factors - the Lehrer article talks about Boston's old basketball court with its uneven parquet floor and dead-spots, which visiting teams did not know about.  Weather conditions can influence this significantly (wind and rain adapted teams will thrive in their own conditions), as can pitch conditions (cricket is a big one for this).

In my experience, familiarity is a really crucial factor, perhaps the main one (though this is just my opinion born of my experiences with the Sevens side).  I believe it reduces anxiety significantly, and even allows players to find visual cues in the stadium that may help their performance.  Much of this happens away from the venue - it's in the hotels, the people, the food, the TV stations in hotels, the sights and sounds.  Just having family and friends around in the build-up is significant, provided it doesn't cause over-arousal.  The key is whether the familiar experience is a positive one or not.  Positive experiences are easy to reinforce, and so a player will be more optimistic, more confident when playing at home.

Experience counts - reducing home ground advantage?

This is why experience is such a vital factor for success in tournaments away from home.  Later this year, the Rugby World Cup takes place in New Zealand, which has historically been an incredible place to win.  There are a number of reasons for this - New Zealand has historically been the world's best team, so really, they'd be difficult to beat anywhere.  But the weather and travel distances don't help, and nor does the psychological block that teams take with them when they go there.  Positive experiences erode these factors, and so teams who want to succeed, will, I believe, have to rely heavily on players who have been there, won there, and know the stadiums, hotels and people.

Whether or not any of the above factors translate to better performance, I don't know, but I guess the bottom line is that playing at home CAN bring what sports psychologists recognize as crucial to optimal mental performance.

But then again, it's still four white lines, a ball and the same set of rules!


The factor I've left out is travel, and that's because it's worth a post of its own, especially given the Super 15 motives behind this post.

That comes tomorrow, so join us then.  Also, don't forget to get on Facebook and Twitter if you're on them - I try to use them as a supplement to the site, posting some thoughts, opinions and links to articles of interest.