Thursday, 2 September 2021

An Overrated Variable

The 2021 NFL season is a little over a week away, with a Thursday night opening game on September 9th, a couple of timely articles by ESPN's David Purdum and Kevin Seifer on the decline of home field advantage. 

If you've been following this blog for any length of time, you will know that taking advantage of the market's over-valuing of home advantage has been a nice earner in certain matches in this sport for many years. Since the league expanded to 32 games in 2002, the record is:
In Divisional games, the ROI increases to 6.8% which over a 19 season period is quite remarkable. Of course last season was unique with limited attendance due to the pandemic, but this decline in home advantage isn't new.
Home teams had a .498 winning percentage in 2020, their lowest since the NFL's 1970 merger with the AFL. But even with full attendance in 2019, they had produced the lowest such mark (.518) since 1972, as well as the lowest cover percentage against the spread (.437) since 1967.

According to ESPN Stats & Information research, in fact, home teams have had a losing record against the spread in 14 of the past 17 seasons. That has happened even as the average spread for home teams dropped 18% in 2015-19 (-2.03) compared to the previous five seasons (-2.47 in 2010-14).
With stadium crowds limited last season during the coronavirus pandemic, home-field advantage dropped to an all-time low, based on the point spreads. ESPN's Kevin Seifert examined how the return of crowds could impact this season in a piece sports bettors should read.

Home teams were favored by an average of 1.10 points last season, by far the lowest average spread for home teams in the Super Bowl era.

Home-field advantage had been declining for years, even prior to the pandemic. From 2015 to '19, the average home spread was -2.03. In the previous 15 seasons, the average home spread was -2.47.

Home teams are struggling to cover even the smaller spreads. Home teams have had a losing record against the spread in 14 of the last 17 seasons, including six of the last seven, and three straight.

"I think it's the market catching up to home field being an overrated variable," Murray of the SuperBook said. "Look how many NFL teams have little if any home field advantage at all. Washington doesn't have a home field advantage. The Chargers don't. I feel like when I watch a Chargers game there's more fans of the opposing team in the stadium. I'm not sure what kind of advantage teams like the Jaguars, Dolphins, Rams, have either. There are a few teams we would say have a real home field advantage like the Chiefs, the Packers, the Seahawks. But there's just as many teams out there that it doesn't seem to make much difference for."

Although articles such as these draw attention to the market's inefficiency, they seem to have little to no actual impact so let's hope for another winning season, even if the four yearly cycle of losing seasons suggests 2021 is due a loss. There may actually be a reason for this, given that the NFL schedule does rotate on a four-yearly basis. 

Although we no longer have the Killer Sports database which made producing a verifiable record of results so easy, I'm hoping to be able to find the time to keep these numbers coming.  

"True investors can exploit the recurrent excessive optimism and excessive apprehension of the speculative public." - Benjamin Graham 

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