What NFL bettors need to know about the value of a conference’s No. 1 seed, the effects of travel, and a little thing called “survivorship bias”
Since 2010, home teams during the NFL regular season (excluding the last week) have been winning by an average margin of 1.9 points per game. The home win percentage was 55.6%. However, we need to dig a little bit deeper and look at the evolution of the home-field advantage — particularly as it relates to our approach to the betting markets.
There is a significant break after the 2018 season. From 2010 to 2018, home teams averaged a scoring margin of 2.33 points per game and won 57.1% of the time. Since 2019, that number has dropped to 0.54 points per game and a win percentage of 50.9%. That’s a difference of two full points. In 2019, away teams even had a positive scoring margin of 0.14, but home teams won 52.1% of the time.
During the COVID season that preceded this one, where most games occurred without fans and almost every game without full stadium capacity, the power of home field was only slightly back. In 2020, home teams won by a margin of 0.14. But this season, home-field advantage hasn’t made it back to previous standards — hosts have been winning by an average of 1.73 points per game.
However, it’s worth noting that it was only 0.99 points after Week 16.
We observed several home blowout wins in Week 17. For instance, the Pats stomped the Jags 50-10. The Packers dominated the Kirk Cousins-less Vikings 37-10. So, as the postseason begins with Super Wild Card Weekend, let’s talk about how much NFL bettors need to adjust how they weigh the value of home field.
Is it Just Noise?
Since 2019, we have had a sample size of 736 games that indicates a decline in home-field advantage. We could see 2019 as an outlier season or simply ‘noise.’ When it comes to the COVID season, we could adjust for the lack of fans in the stadium – even though the sheer number of paying customers isn’t necessarily the biggest driver of home-field advantage.
But even in 2021, home-field advantage wasn’t fully back. At this point, we have to assume that there’s more to it.
There are a few subjective reasons:
- Teams are improving when it comes to traveling. Some units have hired performance scientists to help prepare players better when traveling and reduce stress.
- Offenses are getting better and more innovative. The pass rate on early downs in neutral game states has increased over the past few years, so offenses are more efficient on those downs and don’t have to put quarterbacks into challenging third-down situations as often. (A 3rd and 9 on the road when it’s hard to communicate is quite the task.)
- NFL teams have increased their motion rate before and at the snap. That gives quarterbacks a better tell about what coverage to expect, reduces the post-snap complexity, and exhausting audibles against a loud crowd.
But let’s go even deeper.
Getting the No. 1 Seed is Massive
The playoffs are a different animal, though. From 2010 to 2020, there were 112 non-Super-Bowl matchups in the playoffs. The home team won 62.5% of the time, winning by an average of 4.2 points per game. However, we have to retake a more detailed look:
- Home teams in the wild card round only won 47.8% of the time, and by a margin of 0.65.
- Home teams in the divisional round won 75% of the time, with an average margin of 5.72 points per game.
- Home teams in conference championships won 68.2% of the time, with an average margin of 8.2 points per game.
The home-field advantage seems massive in the divisional round and the Championship game. Home teams in the divisional win more often over a larger sample size which appears to be the peak of home-field advantage.
But we are also dealing with what’s known as survivorship bias.
Home teams in the Divisional Round also happen to be the two top teams in their conference, which meant a Wild Card Round bye for both of them until 2019; now, it’s just each conference’s No. 1 seed. Not only do these teams play in front of their own fans following a week off, but they already one of the best teams in the NFL as a rule.
But even if we adjust for team strength – for instance, via historical prices from betting markets – these teams still outperform that expectation in the Divisional Round.
Pay Attention to “Survivorship Bias”
The top seed in your respective conference means a bye week and home-field advantage throughout the playoffs. This year, that’s the Packers and the Titans. Remember that road teams win more than 50% of the time in the Wild Card Round; Divisional home teams often face opponents on back-to-back road games or even on their third straight road game—the effect for home teams compounds.
Since the decline of home-field advantage in 2019, we still observed almost the same home-field advantage in a limited sample size (eight games) in the divisional round: a 75% win rate and a scoring margin of 6.13 points per game. That includes last year’s 17-3 Bills win over the Ravens and the Saints’ 30-20 loss against the eventual Super Bowl champion Bucs.
Neither team had a bye week.
However, home teams in the Wild Card Round have won only three out of their 10 matchups, losing by an average of 3.9 points per game since 2019.
In general, we are dealing with tiny sample sizes, and bettors shouldn’t overvalue the past two postseasons of data. They should also realize that all the data presented in this article is publicly available. Therefore, most of the information will be priced into the market numbers.
All told, there’s no precise answer to whether home-field advantage in the playoffs changes within the framework of our current season. As a result, bettors have to decide to what degree they accept the hypothesis of home-field advantage being “back” after a two-year drought.