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NFL Home Advantage Is AWOL, but Oddsmakers Aren’t Buying It: Data Viz

lev akabas
·5 min read

It’s easy to chalk up many societal trends of the past two years to the pandemic: Americans fleeing from cities to suburbs, a momentary feeling of mild unease whenever two movie characters get within six feet of each other, and so on. Similarly, the disappearance of NFL home-field advantage seemed to be COVID-induced.

And yet, with crowds back in seats, home teams are 103-104-1 this NFL season, a winning percentage almost identical to their meager 127-128-1 record in front of mostly empty stands in 2020. Throw in 2019, and teams have won just 50.5% of games at their own stadiums over the past three seasons.

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Conventional wisdom says that home-field advantage is worth three points. In reality, the average home team was favored in Vegas by about 2.5 points between 2003 and 2018. That number crept downward in 2019 to 2.0, and yet home teams covered the spread just 43% of the time, the lowest rate in 50 years.

Last season, despite the unique circumstances surrounding fan attendance, bookmakers still favored home teams by 1.3 points per game, but the adjustment was enough to help home teams bounce back and cover 50% of the time.

In 2021, the premium given to home teams by sportsbooks is, for the first time, starkly at odds with recent evidence. Giving an average of 1.6 points, home teams have covered just 44% of games.

The average spread has declined to 1.1 over the past five weeks, compared to 1.9 over the first nine. DraftKings director of race and sportsbook operations Johnny Avello emphasized that oddsmaking strategies evolve weekly, but he maintained that home-field advantage exists. “The fans certainly make a difference,” Avello said. “It’s different for different teams, but it’s worth something to everybody. Your team could be 0-7 at home… and these stadiums fill up. The fans come and support.”

Belief in home-field advantage despite its absence since 2018 is dependent on viewing 2019 as an outlier year. “In 2019, we saw empirically that home-field didn’t really exist, but theoretically it didn’t make much sense to us,” PointsBet senior trader Sam Garriock said. “So while we did nick home-field advantage down slightly this year, we didn’t make it a wholesale change like we did last year when we dragged that thing down to one point.”

The notion that 80,000 shouting fans are meaningless is understandably difficult to accept. “It’s hard to make comparisons back to 2018 and think that something has fundamentally changed,” Garriock said. “With the fans at the same levels as they were in 2018, we can’t quite get there to remove home-field.”

NFL teams are investing more in sleep and traveling to games earlier in the week, to the point where a lengthy coast-to-coast trip may no longer impact on-field performance. Over the past three seasons, road teams are counterintuitively 113-90-1 when playing in a stadium at least two time zones from their own.

The sudden and complete disappearance of NFL home-field advantage is even more perplexing given that most sports leagues domestically and worldwide have come out of the depths of the pandemic with home advantage largely intact.

The NBA has experienced a drop-off in recent years, but home teams are winning more than 55% of games this season—nowhere near the observed NFL trend. “The NFL season is still a really small sample, even across an entire season, so we lean on other sports too,” Garriock said. “We’re probably quite stubborn in terms of moving off of our prior here.”

So are fans and, more importantly, bettors. This Saturday night, the 7-6 Indianapolis Colts will be favored by 2.5 points when they host the top-seeded New England Patriots, who haven’t lost a game in regulation since Oct. 3. “If home-field advantage doesn’t exist, there’s absolutely no way that the Colts are favored there,” Garriock said. “Even if we thought that it no longer existed, the bidders still have a strong belief that it does exist. We’re somewhat beholden to what the market believes.”

Sportsbooks haven’t seen a flood of money on road teams from professional bettors, even though road teams have consistently beaten the spread. “Not all the games that follow that pattern are bad games for the books,” Avello said. “We put up a spread and the customers bet on it. Overall, people say, ‘You might’ve been wrong on that one.’ We might’ve been wrong on the spread, but we [still made a profit].”

Indeed, it’s been a strong year for sportsbooks. Recreational bettors tend to bet on favorites, and underdogs have a winning record against the spread on the year, even after a flurry of down-to-the-wire covers by favorites in Week 14.

Until bettors stop believing in home-field advantage, don’t expect home teams to stop laying points. When it comes to making lines, “really not a lot’s changed, and I don’t think a lot will change,” Avello said.

How long will it take until recent results aren’t seen as a fluke? “It’s a question that we ask ourselves in almost every area of oddsmaking: Do you trust the most recent and valuable sample, or do you trust the large sample?” Garriock said. “It’s a challenge, and it’s one for a real debate I think.”