Referee bias in the NFL

We've hit on this before, but two of the chapters in the outstanding book Scorecasting is on why home teams have an advantage in every professional sport. The book makes the point that it comes down pretty much entirely to referee bias for the home team. Ultimately, the crowd leaves happy if the home team wins, which makes them more likely to return, thus driving up ticket prices, and ultimately making the sport more financially profitable.

So, let's take a look at one point the book makes. It looks at penalties in the NFL. To quote the book:

Quote: Scorecasting

For evidence of offical bias in the NFL, it makes sense to start by considering one obvious component in the control of the men in the striped uniforms: penalties. Home teams receive fewer penalties per game than away teams -- about half a penalty less per game -- and are charged with fewer yards per penalty. Of course, this does not necessarily means officials are biased. Away teams might commit more violations and play more sloppily or more aggressively...

So I looked at the data I have for the NFL for the 2000 to 2010 seasons. Here are the averages per game:

Away penalties: 6.41
Home penalties: 6.03
Away penalty yards: 52.35
Home penalty yards: 49.61
Away yards per penalty: 8.17
Home yards per penalty: 8.23

So, that is a difference of 0.38 penalties per game, 2.74 penalty yards per game, and 0.06 yards per penalty (in favor of the away team).

I think it is hard to make a case based on that alone. As they bring up themselves, maybe it is because away teams are behind more often, and thus playing more aggressively, causing more penalties.

In other parts of the book it argues that referees tend to hide their bias by having calls to the home team's way in crucial situations, and make up for it by having calls to the away's teams way in situations where the outcome of the game is in little doubt.

I'm sure I looked at a different span of time than the author's, but my 11 years shows a smaller effect in number of penalties (0.38 vs. 0.5) and actually more yards per penalty for the home team.

So, my data doesn't exactly corroborate their theory. Just 2.74 extra penalty yards per game does not translate into the extra 2.57 points home teams score on average in the NFL I would say.

I also think the author's play a bit loose with their statistics on the instant-reply challenge, but I won't get into the details. Still, I more or less agree with the author's premise, but I think they are a bit loose with their statistics to make their case, a practice they themselves accuse sportscasters of doing.

Comments?

Great study, Wizard. I never played any professional sports but I did play college football and always wondered if this was true. Playing away is simply more difficult for obvious reasons such as field conditions and different routines. The crowd does play a role psychologically. I have also suspected sideline referee bias towards the team's sideline that they are on.

Quote: RogerKint

The crowd does play a role psychologically.

The authors make the case that in fact, it doesn't. At least in professional sports. As one bit of evidence, they look a free throw percentages. In games the crowd always makes a lot of noise and waves those inflatable batons when the away team shoots, but is still and quiet when the home team does. How does this distraction effect the percentages? It doesn't. There is no significant difference, forgive me if I don't hunt through the books for the specific figures. They also look at field goal success rates in the NFL. Again, no significant difference.

Quote: Wizard

The authors make the case that in fact, it doesn't. At least in professional sports. As one bit of evidence, they look a free throw percentages. In games the crowd always makes a lot of noise and waves those inflatable batons when the away team shoots, but is still and quiet when the home team does. How does this distraction effect the percentages? It doesn't. There is no significant difference, forgive me if I don't hunt through the books for the specific figures. They also look at field goal success rates in the NFL. Again, no significant difference.

But crowd noise does have an effect on effectiveness. False starts must go up for visiting offenses in certain stadiums that are known for their crowd noise(Seattle, Kansas City), as the players cannot hear the QB.

There is also the issue, not of penalties, but of other calls (completions, fumble recoveries), and non-calls going more toward the home team. I don't have any stats, but the refs have other ways of influencing the game besides backing up the visitors.

"So, that is a difference of 0.38 penalties per game, 2.74 penalty yards per game, and 0.06 yards per penalty (in favor of the away team)."

Looking at the figures you have provided, is there any evidence that this affects the outcome of the games? And even if it does, how does this relate to the odds maker's lines in the sportsbook or how could a bettor use this to his advantage?

I believe there was a study done on basketball games that showed that referees were more likely to call more fouls in the second half of the game on the team that the referees called less fouls on in the first half of the game. I did some minor research to see if this gave the bettor an edge, but couldn't not find any positive correlation. I mainly looked at betting the on the team that had more fouls called against them in the first half by betting a second half wager on that team.

Quote: Ayecarumba

But crowd noise does have an effect on effectiveness. False starts must go up for visiting offenses in certain stadiums that are known for their crowd noise(Seattel, Kansas City), as the players cannot hear the QB..

I agree 100%. I'd like to see their numbers off all penalties EXCEPT false starts. Because stadiums put up signs that say "Shhhh..Offense at work" and the like when they have the ball, and encourage a lot of noise when the visitors have the ball. Also, delay of games go up in noisy times, as it takes longer to bark instructions...

This is entirely different than Free Throws; you may be able to concentrate at hit a free throw with extra noise, but if your teammates can't hear what play you are calling, no amount of concentration will make up for their inability to know which route to run.

well didn't really read the thread just kinda skimmed it...BUT....I would not take the opinion of anyone who thinks crowd noise doesn't play a difference....Crowd noise plays a MAJOR factor in the NFL or college football...I can speak from experience....Although I have never play NFL football I did play at the college level and was a offensive lineman for an national championship team....The visiting team will typically have more penlites from two reasons......ONE....the offensive line must operate on silent count making false starts MUCH more common.....Take a look at quest field in Seattle where the Seahawks play...its a matter of pride for the 12th man to be so loud every year that Quest field leads the league in false start penalties for opposing teams......and TWO.....The crowd is quite when the home team offense is on the field...allowing the QB to use a hard count and draw the defense off sides.....

Plus you will just always play better at home.....for many reasons most of which psychological.....Just the fact that you woke up in you own bed that morning and had breakfast and coffee in your own kitchen....instead of waking up in a unfamiliar hotel room....its had to explain but you just feel much more comfortable playing a home game than a road game......and you DO feed of the crowd especially on the defensive side of the ball....

Quote: vert1276

Just the fact that you woke up in you own bed that morning and had breakfast and coffee in your own kitchen....instead of waking up in a unfamiliar hotel room....its had to explain but you just feel much more comfortable playing a home game than a road game.

The book also says this plays an effect. As I recall, it said that when a team plays a road game, but very close to their own homes, that home field advantage almost disappears. For example, in cities with two baseball teams (New York, Chicago, SF/Oak).

Quote: Wizard

The book also says this plays an effect. As I recall, it said that when a team plays a road game, but very close to their own homes, that home field advantage almost disappears. For example, in cities with two baseball teams (New York, Chicago, SF/Oak).

Ya I would agree...playing a road game close to home is easier....the worst is if you were from the west coast(as I was) and then having a 10am start on an east cost road game....it like playing at 7AM to you......But like I said before crowd noise is the big reason....not only for penlites...but it is just much more difficult to play offense on the road....the crowd noise means the QB will have a harder time calling audibles and will have to use hand signals...which will restrict what he is able to call.....The lineman calling the protection schemes on the line(normally the center but not always) will have a MUCH harder time making protection call's.....It is MUCH more difficult to run a no huddle offense on the road becasue of of noise.....I could go on and on......Its just a lot harder to play on the road.....

Of course none of this means anything if the road team can jump to an early lead and "take the crowd out of the game" which of course was always our goal.....I didn't really mind road game....offensive lineman kinda like them LOL.....it just means becasue of crowd noise you are going to end up running the ball more....And any offensive lineman would rather have the offense run than pass....:)

Home field advantage? I can think of some...

Arena familiarity. At my home field, I know every inch of it. Where it's muddy, where it's drier. Whether it's hard and rocky, or soft and supple. Whether a mean cut is going to cause me to slip and fall or dig in and go. I know when we get in the red zone where the baseball field cuts through, that "dirt" is going to be sandy and loose, not like dirt at all. In hockey, I know our boards are "soft". You have to adjust angle and velocity when passing off the boards. I know it's sometimes wet behind the visitors net early in the game and the puck sticks. Our ice feels soft, like you can dig into it, yet Jamestown's feels like skating on marble. I know the puck has a habit of catching an edge and careening to mid ice when you rip it along the boards. All this info is something the visitors don't know, and I know I have a harder time adjusting when playing away, especially on board play. I try to dump it mid ice and the puck rockets off the boards for icing. For me, this is the biggest factor when playing home vs away, knowing your battlefield.

Refs. Does the NFL rotate the crews evenly all over the place? I ask because we don't. The crew stays at that particular arena. So for our guys, I know that Jim Bob's crew is going to call every little thing, while Steve Dave's crew will let me get away with murder. When we go away, I have no idea until it's too late. If the NFL likewise keeps crews in certain areas, and say Jeff Tripplett does a lot of West Coast games, the West Coast teams would conform to his type of calls and may be vulnerable once they move to the land of Ed Hochuli.
Plus, professional or not, they're human. No one could tell me that not once does a cheer or jeer from the crowd influence a decision. I highly doubt it's on the regular, I even suspect it's rare, but I refuse to believe it doesn't happen at all. Even if it's one call in every 50 games or one call in every 5,000 plays, that makes a difference. Maybe the difference that's seen by your numbers.