Will the 2020 NFL season see the death of home-field advantage?

The sports betting community is set to handicap an NFL season that will look -- and sound -- different than anything we have ever witnessed. Nearly empty stadiums make for just one variable that a coronavirus world presents, and accurately projecting its impact will prove to be a difference-maker for everyone's bottom line.

Home-field success waning

The assessment begins with a concept that already seems to have become outdated: home-field advantage. In fact, home teams won just 52% of regular-season games last year. That ranks as the third-worst season in the Super Bowl era (since 1966) and worst since 1972.

Additionally, point spread results indicate a recent regression that suggests that perception has yet to adjust to reality. Home teams have a below-.500 cover percentage in five of the past six and 13 of the past 16 regular seasons. In 2019, home teams covered just 43.7%, which was the worst of any season in ESPN's database (since 1966). That came in a year when home teams were favored by only an average of 1.76 points, which ranks third lowest all time.

"Fans just don't matter that much. If I had a home-field advantage worth 2.0 points (on a projection), I am using 1.5 this season. So it's about 75% (without fans). Other people are using about 50%, but I think that's too much the other way," ESPN sports betting analyst and professional bettor Preston Johnson said. "On top of that, we have four months of international data in baseball and soccer (without fans this summer) that shows home-field advantage is not that much. Fans just don't matter that much."

But what about those three points?

Casual betting conversations routinely reference the home field as worth three points to the spread, but that has never truly been the case. Oddsmaking is much more advanced and nuanced than simple math. Everything is predicated on "key numbers," which are three, four, six and seven in the NFL. They are correlated to the sport's scoring of field goals and touchdowns and common margins of victory.

"These key numbers are so important. It's not like college, when you have totals between 60 and 80 and (a half-point or point on sides) really doesn't matter. One team winds up winning the game by double digits almost all the time," Westgate Las Vegas SuperBook vice president of oddsmaking and risk management Ed Salmons told ESPN. Over the past five years, a league-high 14.7% of NFL games were decided by exactly three points. The second-most common margin of victory was seven points (9.9%), followed by six points (7.1%).

Both sides of the counter have learned to accept the nature of the beast. Key numbers play a vital role for bookmakers and how they manage a sportsbook's position on each NFL game because of how professional bettors interpret value. "Oddsmakers are much better at anticipating where the number is going to close than years ago. You're handicapping betting behavior more than anything, especially on the higher-profile games," Salmons said.

In short, key numbers trump any rationale or breakdown of stadiums with minimal fans. Over the past five seasons, there were 470 NFL games with a favorite of -2, -2.5, -3 or -3.5. The favorite won by exactly three points 47 times, or 10%. "I don't think people are running around and saying because there's no crowd, instead of making the line -3, let's make it -2," Salmons said. "Three is the key number. Everybody knows that."

Road hurdles lowering

Additionally, performing well in road games has become less difficult, thanks to the advancement of private air travel, football technology and mental fortitude. "You have talking headsets now in helmets, and you have signals from the sideline ... and [players] are just more experienced than they ever were before," Johnson said. "On top of that, on the sports psychology side, these guys are trained and prepped more than ever to be more sound and to block out crowd noise."

The NBA, WNBA, NHL and MLB are already playing without fans. From the onset, LeBron James expressed reservation about empty arenas. "It's been a very long time since no one has been watching me play the game. I'm just trying to find that rhythm and lock in," James said Aug. 8, following the Lakers' fourth loss in their first six bubble games. "You have to really love basketball to be here because there's no extra motivation, you know, as far as that you get or the excitement from the crowd and things of that nature."

As the 17-year NBA veteran and four-time MVP indicated, players sense crowd noise and often feed off it. The Minnesota Vikings own a league-best 28-11-1 ATS home mark the past five years, perhaps fueled to a certain degree by Skol chants. "The crowd usually gets really loud for the defense in the red zone. If you look at a team like Denver, they were really good in the red zone at home," Caesars William Hill oddsmaker Alan Berg told ESPN. The Broncos led the NFL last season by allowing only a touchdown on 39.13% of red zone opportunities, and the Vikings' defense has ranked in the top three for three straight seasons.

Home-field advantage obviously involves more than a roar or manufactured entertainment, such as familiar public address announcers and other ambiance. Denver will still have its altitude, warm-weather teams still must endure late-season elements, and travel will still involve challenges and annoyances that figure to inhibit a team's performance.

"I think it's more of a travel situation. The [Los Angeles] Rams going to play the [New York] Giants is different than [Chicago] Bears to the [Detroit] Lions," Berg said. "With an element of COVID, I imagine traveling won't be the most fun part for these teams."

Home dominance correlates to rosters

What about notorious stadiums that seemingly demonstrate a significance? The New Orleans Saints certainly offer an intimidating environment, especially with the enhanced acoustics of a domed stadium. The Seattle Seahawks and Kansas City Chiefs carry similar daunting reputations. However, that could all be a case of confirmation bias.

"That's more the correlation if a team is good. The [Oklahoma City] Thunder had one of the best home-court advantages when they had [Kevin] Durant, [Russell] Westbrook and [James] Harden because the team was good," Johnson said, referencing the trio that reached the 2012 NBA Finals before breaking up. "Everyone is pumping up Arrowhead Stadium, but they have [former league MVP and reigning Super Bowl MVP Patrick] Mahomes, so they're really good. It's tough to play good teams."

The Seahawks began a five-year run in 2012 that included at least one playoff win each season and back-to-back Super Bowl appearances. Seattle's regular-season home record was 34-6 in that span. As the team lost key members of its vaunted "Legion of Boom" defense, the Seahawks have mustered only a 14-10 home mark the past three years.

Let's talk the 2020 NFL season

Is it time to rid ourselves of the vernacular? Not yet. Home-field advantage is still an accepted concept, but it is time to reconsider some betting axioms. The past 10 seasons, home underdogs are 437-438-20 ATS for a 49.9% cover rate. Home 'dogs in prime-time are 88-84-4 ATS (51.2%). Double-digit home favorites are 114-114-2 ATS (50.0%).

Specific to this opening weekend, the Lions (-2.5) are hosting the Bears. If all of a sudden Ford Field allowed full capacity, the line would not increase to -3. If it did, sportsbooks would draw steady wise guy action on the underdog because of being able to push their bet on that key number. But other games that do not hover around a key number would be more likely to move, if fans were added. The Seahawks (-1.5) are road favorites against the Atlanta Falcons. That number would probably move to PK with a full house.

Stadiums without fans could ultimately translate to a whole lot of nothing. Crowds are one small piece to the giant puzzle. Society has caught up -- and so have oddsmakers.

ESPN Stats & Information researcher Mackenzie Kraemer contributed to this article.