For a long time, if you asked any regular NFL bettor what home-field advantage was worth, you more or less got the same answer: three points on the spread. But the collective understanding of what the home field is worth today has evolved rapidly due to a long-standing downward trend, as well as adjustments suggested and made during the nearly fanless season of the COVID pandemic.
Many analytical bettors and analysts have kept a keen eye on home-team performance in the last two seasons following the full return of fans. So how did things exactly shake out? Do we have a clearer understanding of how much home-field advantage is worth today?
Resetting the table
In 2019, home teams won just 52.3% of games (the second-lowest mark at the time), and their average scoring margin was just 0.1 points (the lowest mark at the time). Their spread cover rate was also just 43.1% despite the average home line plummeting down a half point from the previous season (-2.5) to a new all-time low of -2.0.
Then, in the COVID-stricken 2020 season, things got worse. The average home line dropped to -1.3, which was the first time in 20 years the average home line dropped in consecutive years. The drops from 2018 to 2019 and the subsequent drop from 2019 to 2020 were also the two largest during that span.
The shifts in the market and home-team performances had many bettors and analysts claiming that home-field advantage was effectively dead prior to the 2021 season — a sentiment that carried over into the 2022 season. But considering the exceptional circumstances of the 2020 season (with little to no fans in attendance) and in anticipation of the presence of fans having at least some effect, we warned against that line of thinking.
Understanding the change, setting the expectation
So what parts of diminishing home-field advantage were noise, and which held weight?
Disadvantage from travel
The mental and physical tolls of traveling have eased over time. Whether it's the travel itself becoming less taxing, the hiring of sleep scientists to optimize sleep schedules, or improving technology enhancing game preparation during travel, there are plenty of reasons traveling teams are at a much smaller disadvantage than they were in previous decades.
Referee bias
Some data supports the notion that referees are inherently biased towards home teams, most likely due to the pressure to appease home crowds. In the three seasons before 1999, home teams had a 62.0% win rate and 52.6% cover rate. Then, in 1999, the NFL introduced challenges and instant replay. In the three seasons following the change, the home team's win rate dropped to 56.9%, and their cover rate dropped to 49.7%.
Fans affect footbal
A study by Ben Caterine of the Northwestern Sports Analytics Group further supports the notion that fan presence impacts performance.
In said study, Caterine examined home team performance during the 2020 "COVID" season during which fan attendance was allowed to varying extents. He found that home teams won 54% of games when fans were allowed and only won 47% of games when no fans were permitted.
Ignore 2020 season
All in all, we concluded that the 2020 season was an extreme outlier and worth ignoring. And when examining and paying respect to home-field advantage trends dating back to 2007, we predicted that the average home line would land around -1.9.
So how did we fare?
2022 in review
When looking at Weeks 1-17 (Week 18 featured an abnormal amount of data-skewing spreads due to many teams having nothing to play for), the average home line during the 2021 regular season was -1.8, and it was -1.4 in 2022. In 2021, home teams won 51.8% of the time, won by an average of 1.7 points, and covered 48.0% of the time.
In 2022, those numbers were 55.8%, 1.9, and 51.2%. Here is how those average home lines have compared to each season since 2007 (but again, excluding the 2020 season):
| Year | Average Home Line | Delta vs. PY | Three-Year Rolling Average | Line vs. Rolling Average |
|---|---|---|---|---|
| 2007 | -2.6 | -0.4 | -2.77 | -0.17 |
| 2008 | -2.6 | 0 | -2.77 | -0.17 |
| 2009 | -2.7 | +0.1 | -2.73 | -0.03 |
| 2010 | -2.5 | -0.2 | -2.63 | -0.13 |
| 2011 | -2.6 | +0.1 | -2.60 | 0.00 |
| 2012 | -2.4 | -0.2 | -2.60 | -0.2 |
| 2013 | -2.6 | +0.2 | -2.50 | +0.1 |
| 2014 | -2.6 | 0 | -2.53 | +0.07 |
| 2015 | -2.1 | -0.5 | -2.53 | -0.43 |
| 2016 | -2.3 | 0.2 | -2.43 | -0.13 |
| 2017 | -2.3 | 0 | -2.33 | -0.03 |
| 2018 | -2.5 | 0.2 | -2.23 | +0.27 |
| 2019 | -2.0 | -0.5 | -2.37 | -0.37 |
| 2021 | -1.8 | -0.2 | -2.28 | -0.47 |
| 2022 | -1.4 | -0.4 | -1.65 | -0.63 |
"Why since 2007?" you may ask. That is when the trend began of the yearly average home line becoming lower (or closer to zero) than the three-year rolling average (the average of the three years prior). "Why is that significant?" you may also ask.
It signifies that the year-over-year decrease in home-field advantage is outpacing (rather sizably) the more moderate three-year trend. The chart above shows that the average home line has been lower (or closer to zero) than the three-year rolling average in all but three of the last 14 seasons (2013, 2014, and 2018).
Home-field advantage in 2023
So, what should we expect in 2023? Last year featured the third-largest year-over-year decline in the average home line, barely being beaten out by the declines in 2015 and 2019. But when looking at the delta in the three-year rolling average, the -0.63 decrease is sizably the most significant with the next largest decline being the -0.47 in the year prior.
Given that now three of the four largest declines in the rolling average have occurred in the last three years, we should expect some stabilization and regression rather soon.
For that reason, we would expect the average home line to be -1.4 for the 2023 regular season.
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NFL home-field advantage FAQs
While home teams are generally still favored to win NFL games, their average home line has been coming down over the past decade.
The average home-team point spread was -1.8 in 2021, implying that home-field advantage was worth just shy of a point in 2021.
