When figuring out what the line should be for any given matchup between two teams, there are a few steps to take. First, you determine each team's value in relation to an average NFL team, Patriots are five points better than average and the Steelers are three points better than average, you'd make the line Patriots -2 if they played on a neutral field.when discussing how to build a power ratings system to help beat the books. Once you have a number for each team, you use the difference to determine what the line would be if both teams played on a neutral field. For example, if the
The next step is what we'll discuss today: adding home-field advantage to your matchup. Historically, home-field advantage has generally been assigned a worth of three points when figuring out the line for a matchup. In our Steelers at Patriots example above, that would make a line in Foxborough Patriots -5. Some teams have been so money at home against the spread -- the Patriots and Seahawks are both near 60 percent ATS at home since 2003, for example -- that some people add a half-point here or there when it's believed to be warranted, but for the most part, if you have two even teams, you'll see the home team favored by three points.
It probably won't shock you to know that smart bettors don't take this three-point rule at face value, and those that dig into the numbers know that home-field advantage has actually been worth far less than three points on average around the league. Warren Sharp recently broke down why this could be the case on his website, with potential reasons ranging from improved viewing experience at home to improved travel and sport science by NFL teams and more. For our purposes, the why doesn't really matter. Just knowing that it's happening is key to getting an edge.
Forget the why. What really matters to bettors is: how much?
Calculating home-field advantage (2014-18)
Each offseason, I put together a weighted home-field advantage (wHFA) formula that takes points scored and allowed over the last five years for each team and gives a diminishing weight the further you go back in time.
(While I think other data exist that is better for predicting future performance than points scored and allowed, the benefit of using these numbers is that we're already dealing with the scale we want to use for our final output. Otherwise, we'd have to find a way to calculate a conversion rate for another stat to points scored to help us determine what it all means for our point spreads.)
The results on a team level are pretty striking, and we'll get to them in a minute. But for the league as a whole, wHFA calculates that an average home-field advantage in the NFL is 2.31 points, which is just 77 percent of the three-point standard.
Perhaps this overestimating of home-field advantage is why just nine teams covered more than 50 percent of the time at home last year (playoffs included), with 15 teams below water and eight teams right on 50 percent. More teams topped 50 percent than did not in 2016 and 2017, so it's also possible this is a one-year blip. But wHFA also came in well below three points last year, and the year before, so don't be surprised if books shade away from a three-point standard on average.
Below, you'll find a table with every team's wHFA from 2014-18, then what I'm estimating that team's home-field advantage will be in 2019. I'll be using these numbers along with my power ratings each week to determine what I believe the lines should be at the beginning of the week. If there's a large discrepancy between my line and the posted line, that's an indicator it's time to make a move.
I'll cover some specific cases after the table, but for now, the data:
Accounting for Browns excitement
The first curious 2019 number might be for the Browns, who are given 2.5 points at home despite a wHFA of just 1.18. Here's the thinking: for years and years, going to Browns home games must have felt like a chore rather than a reason for hope. After all, this team won just once over a 37-game stretch from 2015-18. How excited would you be dealing with loss after loss?
But optimism abounds in Cleveland in 2019, with the Browns favored to win the AFC North all summer after an influx of top-tier talent, most notably Odell Beckham Jr. We're going to see a much different Cleveland crowd at Browns home games as the franchise chases its first division title since 1989. That was so long ago, current franchise savior Baker Mayfield was negative-6 years old.
Dolphins still unbelievably great at home
When I, I talked about how the Dolphins were surprisingly the best team in terms of wHFA in the league. There aren't many people who would consider the Dolphins an elite home team, and I think that's largely because they've been so bad on the road, it's lowering how we grade the team overall and causing them to be underrated at home.
After checking in with a league-best 5.45 wHFA last year, the Dolphins blew that number out of the water this year, and their 6.91 wFA means they're nearly seven points -- seven points! -- better at home. How does that happen? The offense has been putrid on the road, and last year's 5.7-point difference between home and road is actually a three-year best for the offense. On defense, it's more of the same, with the team surrendering almost 11 points per game more on the road.
I'm not telling you to give the Dolphins seven points of home-field advantage. But I am comfortable making them one of four teams with a four-point number for 2019 along with the Patriots (surprise), Packers and Raiders.
Yes, the Raiders have turned in one of the wHFAs for 2019, thanks in large part to extreme offensive splits over the last two years. But with a scheduled move ahead in 2020, how should we treat this team for their final year in Oakland?
For some teams making a move, I would definitely downgrade their home-field advantage due to hard feelings against the franchise and potential abandonment by the fan base in a down year. Somehow, I don't think that's going to be a problem in the Black Hole, where they should be fired up for each and every home game in the final season. It's a situation worth monitoring as the season moves along, and I'll revisit my home-field rating depending on how their crowd responds early in the year.
Better on the road
Another interesting development is that five teams have actually been better on the road over the last five years than at home. That group of five is lead by the Giants, who played much better away from MetLife for the second straight year, resulting in a negative-2.22 wHFA. Note that I wouldn't actually give a team a negative home-field advantage when figuring out a 2019 number, but the Giants sure make a strong case.
Four of those five better-on-the-road teams have my lowest 2019 number at 1.5: the Giants, Lions, Rams and Redskins. The Lions were better on both sides of the ball on the road last year, particularly on defense, but that could be a one-year blip. The Rams were actually better at home last year but are still paying a price for their 2016-17 numbers. Washington has been worse at home than on the road in each of the last three seasons, and as a result, you can make an argument to put them at one point.
The Saints are the fifth team underwater in wHFA, thanks largely to the defense performing better on the road year in and year out. Though most would likely consider them one of the stronger home-field teams, their ATS +/- over the last five years is negative-2.4, tied for fourth-worst in the league over that span. I'm only giving them two points of home-field advantage for 2019, and there could be value going against them on the spread if that assumption of being a great home-field team continues to hold.
Don't get carried away
Just because we saw one extreme in 2018 doesn't mean it has to continue for a team in 2019. The Jets were the only team other than the Dolphins to check in with a wHFA over 5.0; this year, that number is closer to 2.0 after a rough year for the defense at home. The Patriots played about the same on the road and at home in 2017, leading to a wHFA number of 1.36 last year; this year, they're back to being one of the best in the league.
My numbers are certainly better than just giving the home team three points in every game. But they're not perfect. If you use them to help stay ahead of the books, great. If you use the ideas behind them to put together a better system, even better.
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