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May 6, 2011

United Will Win on Sunday… Here’s Why

The above video is from Palermo’s visit to Catania in February 2007. The Sicilian derby—and that 06/07 season marks the first time the derby was contested in Serie A in 44 years—was suspended for over 40 minutes when CS gas drifted over the pitch (you can see players squirting water over their faces as they are tearing up).

After the match—won by Palermo 2-1—Catania supporters clashed with local authorities; and, during the urban melee, police officer Filippo Raciti was killed in the violence.

The video also explains why United will beat Chelsea on Sunday.

It only makes sense people.

In the aftermath of the riot and death of Raciti, the Italian Football Federation decided to enforce the Decreto Pisanu, a law requiring Italian football clubs to meet safety standards in their stadia. The law had actually been on the books for two years, but was almost entirely ignored. As a result of the enforcement, games at Fiorentina, Livorno, Napoli, Verona, and a handful of other venues across Serie A and Serie B would be played without spectators until the stadia met with safety requirements (Catania was banned from playing in their stadium at all and had to move its remaining matches to a neutral site).

In total, 25 matches were played in Italy over the following weeks without spectators.

Two Swedish economists took the data from the matches played in front of empty stadia and compared it to those from normal matches with crowds—the Italian Football Federation had essentially created a lab with a control group—to demonstrate something most sports fans think they know to be true but can’t really prove. Specifically, that the home teams get the calls. They are whistled for fewer fouls, they receive fewer yellow cards, and fewer red cards.

And the size of the difference is not trivial.

For example, in the Italian sample, on average the number of fouls called against the home team with a crowd versus without a crowd is 19.26 to 20.43—just over a foul a game. Small yes, but bear with us. The respective difference for the away team is 19.41 to 16.62. Less small (think about getting as many as three extra free kicks around the box). So the difference of the differences (1.17 – (-2.79) ) is 3.96.

That means that the bias in favor of the home team is 23% (or (3.96/16.62)*100)). Similar calculations for yellow cards and red cards show the bias in favor of the home team at levels of 26% and 70% (!) respectively. Basically, you have to Shawcross someone to get a red card at home.

The paper, found here (warning PDF link), shows clear statistical evidence of referee bias as a result of social pressure. The pressure in this instance is the home crowd. Even when controlling for player outcomes, the results were still statistically significant.

In other words, the authors looked at player variables—shots on target, shots off target, number of tackles, tackle success rate, passing accuracy, and ball possession—across games with crowds and games without to see if players played differently in front of an empty stadium. They didn’t, which basically allows the authors to say that the differences they saw in fouls and cards were because of the referee and the referee alone.

It’s not surprising to find that home teams get the calls but to see it spelled out mathematically is pretty startling.

The effect of this social pressure on referees is also observed in the negative. In the Bundesliga several of the stadia are also used for athletics. So there is a track between the crowd and field. Recall that sound decreases with the square of the distance, so it doesn’t take a huge distance to abate some of the volume of crowd noise.

And in those Bundesliga stadia with a track acting as a buffer between the crowd and the pitch, the referee bias for the home team was observed to be about half of what it was in the rest of the Bundesliga, and the whole of Europe for that matter. (Memo to West Ham: Renege on your promise to keep the track at the Olympic stadium).

This couples well with a couple of other studies. One is the “Fergie Time” paper. The original research was done by Luis Garciano and Canice Prendergast (that’s a dude, by the way) and was done with matches from La Liga. What they found was that when the home team was trailing, on average more injury time was added (referees were giving the home team more time to score and salvage points); but when the home team was winning, less injury time was added on (referees were denying the away team time to possibly level or win).

As important, they didn’t just find the difference, but they found was the difference was more pronounced the larger the crowd. Given that’s the case, it would stand to reason that, at Old Trafford—the largest stadium in the Premier League—the effect of either lengthening or trimming stoppage time depending on the score would be greatest. Fergie tapping on his watch probably doesn’t hurt.

A second study, done in 2001, showed taped professional soccer matches to two groups of officials. One group got the match with the sound of the crowd, the other group had no sound at all. The group with sound made calls that were more consistent with the actual calls that had been made on the field. Additionally, the refs watching with sound also exhibited more anxiety and stress. That just from watching a replay.

Referees are indeed human (probably unfortunately it turns out), it only makes sense that they are susceptible to crowds and that they would err on the side of alleviating the stress the crowd would be causing them.

Think back to Arsenal’s collapse at St James Park earlier this season. Diaby was sent off in the 50th minute. Newcastle were awarded a penalty in the 68th. Then they scored again in the 75th to make it a 4-2 game with a man advantage and 15 minutes left to play.

After the 80th minute, when the crowd at St James Park—the third largest stadium in the Prem—was on the verge of mayhem as they sensed a full comeback, match official Phil Dowd called six of the match’s 15 fouls against Arsenal, one of which was a phantom PK, in addition to issuing a yellow card to Barcary Sagna. That’s 40% of the fouls in about 11% of the match.

On the other end of the pitch a potential game winning goal for Arsenal was erased when Robin Van Persie was flagged (and by all video evidence incorrectly) for being offside.

Again, that’s just the last ten minutes. Given the data collected in Italy, it’s hard not to conclude that Phil Dowd displayed bias to Newcastle because of the crowd. And really, they went ballistic every time Joey Barton hit the ground whether he had been touched or not. But we’re not bitter.

Or think back just to this past weekend. A linesman in no position to make the call, awarded a goal to Chelsea against Tottenham on Gomes’ frango even though replays seemingly show the ball never fully crossed the goal line. The game was at Stamford Bridge (where the fans sit right on top of the linesmen). The crowd erupted as the ball inched toward the line. The linesman gave the goal.

So, yeah. People can point to Howard Webb and say he’s in the bag for United this weekend. Truth is any referee is in the bag for United at Old Trafford, just as is any official for the home side. And the larger the crowd (where size is used as a proxy for loud…) the more in the bag they generally are. And they’re not even aware of it. It’s obviously not a conscious decision, but all evidence points to the fact that any official would favor United on Sunday.

In fact in the biggest moments, there’s prima facie evidence they already do. Using penalty kicks awarded as a proxy for “biggest moments”, United’s home record is pretty incredible. This season they have only conceded one at home in league matches.

Compare that to the rest of the top four: Chelsea – 2, Arsenal – 3, Man City – 2.

It doesn’t seem that startling until you add a few more years to the total. Last year (the 09/10 season) the other top four finishers conceded (and this is just at home and just in league matches) as follows: Chelsea – 1, Arsenal – 3, Tottenham – 3.

United conceded zero.

In fact, since the 07/08 season (inclusive), opponents have been granted all of three (3) penalty kicks at Old Trafford. And curiously, two of those three were given to Liverpool. Think about that: over the course of the last 76 league matches, clubs not named Liverpool have been granted exactly one spot kick at Old Trafford by the officials. For comparison, over the same time period, opponents have been granted nine (9) penalty kicks at the Emirates.

You can talk about the quality of United’s center backs—and they have one of the best pairings in the game—but it’s silly to think that, as a squad, United have only committed three fouls in the box over the last four seasons (just as it’s silly to think Arsenal have only committed nine…. it’s just that the former is an order of magnitude sillier than the latter).

Two final notes. Much of the information on officials and crowds is cribbed from a book called Scorecasting (Moskowitz and Wertheim). I highly recommend that you either read it or you do everything in your power to avoid it. It has changed the way I watch sports, and not for the better. It pretty much destroyed my ability to watch MLB. Hell, now I can call a borderline pitch before the homeplate umpire with an uncanny accuracy (where accuracy isn’t what the call should be, but what the umpire actually rules). Still, it’s worth a look. It might not seem like great insight to say “home teams get calls” but the book is way more thorough and it goes deeper to show that officiating bias is the reason that explains homefield advantage (as opposed to things like familiarity with stadium, sleeping in your own bed, the crowd willing you to a better performance, etc.).

Second, I say that United will have a huge advantage in that the official will favor them in many calls but remember last season Dideir Drogba was three yards offside when he scored what could be considered the goal that gave Chelsea the title.

That match was at Old Trafford. Ref blew it. And he blew it in favor of the visiting side.



About the Author

Precious Roy





30 Comments


  1. I can’t remember what book it was in, it may have been Soccernomics, but it said that in international matches home teams averaged an extra .3 goals per game I think it was, which certainly adds up over time


  2. So, the results are just fated, no chance, no choice, just destiny?
    /drinks.


  3. bergkampesdios

    NYK and PR have laid down a gauntlet today. Well done, sirs.


  4. MP

    I read that entire piece and was waiting to unleash my bombshell rebuttal (even if it was only a single sentence and a terribly small sample of data). Then PR’s last two paragraphs ruined all my fun.
    .
    Agreed with berg, great work today guys. Couple of real good reads…


  5. Han-ball

    Someone reads Sports Illustrated…
    Nicely done though. This place is becoming almost second rate.


  6. who reads SI?
    /has a subscription and reads it about three times a year not including the swimsuit issue which i don’t really read as much as ogle.


  7. Jesus. Well done, PR.


  8. Han-ball

    TFA: I do! And I’d bet PR does too.


  9. MountainWag

    PR, great read. I enjoyed it, though I will be perpetually depressed because I know in my heart of hearts Arsenal will never get THAT much of an advantage at home because unless it’s a rout (by us), our crowd is busy napping, knitting, or generally eating somewhere other than cheering for the team. Stats, BE DAMNED!


  10. Precious Roy

    Han-ball: Haven’t in years. But Wertheim in a SI scribe, so it’s likely he’s put some of the stuff in the book in SI (and vice versa).

    MW: I can’t be a total hypocrite. I’m sure Arsenal get the better of the balance of the home calls. But some calls that went against us at home (or didn’t go in our favor) this season are still baffling. That said, the Emirates can be (and often is) moribund, so home fans are pissing away what could be a bigger advantage. Remember people talking about the atmosphere at the home leg of the CL tie with Barca and we seemed to get a few decisions in our favor that night.

    In fact, if Gazidis and Co. lowered ticket prices (instead of the increase they just announced) and somehow facilitated the drunkest and rowdiest sitting closest to the pitch, the club might make more money by winning more stuff (the logic being: louder crowd equals more ref decisions in our favor means more points means trophy). But that’s a gamble they would never take. Also, designing the stadium to where there are acres of space behind the goals before the stands start up was a design failure that is working against the club.


  11. Han-ball

    PR: Interesting. They must have, because the same three studies you cite are the ones he cites in SI, which I guess is just a small version of the book.


  12. Precious Roy

    Yeah, Han-ball I made sure to clearly credit Scorecasting in the post, but tried to go back and find the original studies. There was another by some guys in the UK and a Kiwi but it involved a bivariate negative binomial regression, so it’s a little less user-friendly. It still supports the premise of home-team ref bias. I couldn’t find the Prendergast paper either, but he’s actually a former professor of mine, so I should just email him and ask for a copy. Funny thing, he used to ask soccer-specific questions on some of his homework assignments (he’s a labor economist) but I guess was too stupid to make anything of it.


  13. Prendergast’s publications are interesting…very much looking into bias and favoritism.


  14. Precious Roy

    Well crap… never occurred to me to go to his page on the school’s site. The damn thing is right there. I was using Google. Told you I was too stupid.


  15. weird that google wouldn’t pick that up though.


  16. Precious Roy

    My search terms were also stupid.


  17. Lennon's Eyebrow

    Lolwut? Moar dick and fart jokes plz.


  18. Lennon's Eyebrow

    But seriously, y’all have done some really good work lately. (bat-post aside)


  19. @LE: Why do you make me sad?


  20. Goat

    Anyone up for a final exam liveblog?


  21. Goat

    This 8-11 final is bullshit. I’m not going to be able to stay awake much longer.


  22. Ryan

    Ouch. 8-11 finals? I think the latest here are 7:25-9:25.


  23. Goat

    @Ryan: Yeah, it’s new this year. This is also the class that has been fucking up my Tuesday Champions League viewing so I really hate them.


  24. @Goat, you have to at least have a few kids who are watching Champions League games in your class right?


  25. Goat

    @Brian: One guy claims to be a Barca fan but from my limited conversations with him he seems to not pay much attention. But other than that, everyone else is too enthralled by my lectures.


  26. Suckers, they clearly do not understand the importance of the Champions League


  27. Ryan

    Timbers time!


  28. Ryan

    Decent number of empty seats tonight. I love the high wall left over from the baseball stadium. Gives it a sort of Bundesliga feel for me.


  29. it involved a bivariate negative binomial regression
    That gave me wood



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