Sports

Did the Pandemic Solve One of Sports’ Weirdest Mysteries?

Home-field advantage is real. Why?

The Lakers hug one another on a gym floor.
The Los Angeles Lakers celebrate after winning the 2020 NBA Championship in Game Six of the NBA Finals at AdventHealth Arena in Lake Buena Vista, Florida on Oct. 11. Mike Ehrmann/Getty Images

One of the few things sports fans and those who study sports for a living absolutely agree on is that home-field advantage is real. The advantage is sometimes presented in clichéd terms—“You don’t wanna play the Packers at Lambeau in the snow!”—and other times laid out empirically. The truisms and the data reinforce each other.

In their 2011 book, Scorecasting: The Hidden Influences Behind How Sports Are Played and Games Are Won, Yale behavioral economist Tobias Moskowitz and Sports Illustrated writer L. Jon Wertheim pulled decades of data from seven sports and 19 different leagues or levels of play. In each, the home team had won a solid majority of games over the previous decade, from 54 percent in Japanese Nippon League baseball to 69 percent in college basketball.

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In the years since that book came out, the overarching picture of home-field advantage hadn’t changed, with home teams continuing to post win rates well north of 50 percent. And then COVID-19 altered where, when, and how sports were played. For the first time, leagues across the globe have played long stretches with no or few fans in the stands, and, in some cases, they’ve relocated their games to neutral sites.

Given the ubiquity of home-field advantage, it’s surprising that there’s not a real consensus about what causes it. The pandemic—when some leagues played at neutral sites and some did not, and some teams played in front of fans while others did not—provided a number of controlled experiments to test the leading theories.

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The results of those experiments have been striking, both because of what they’ve confirmed about home-field advantage and what they’ve left uncertain.

• In playoff games in the neutral-site, fan-free NBA bubble, designated “home” teams went 39–44, a massive drop-off from the mid-60s winning percentages NBA teams generally post in the playoffs when they’re playing in their actual home arenas in front of actual fans. In the early weeks of the NBA’s new season, which is being played in empty or mostly empty home arenas, home teams are trending toward their worst win percentage ever—just a shade over 50 percent.

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• The WNBA held its entire 2020 season and playoffs in a neutral-site, fan-free bubble, and designated “home” teams went 74–73. “Home” teams were winning 62 percent of their bubble games about a month into the season, to players’ and coaches’ bewilderment, before the numbers evened out. (In the prior season, actual home teams won 60 percent of the time.)

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• In the NHL’s neutral-site, fan-free playoff bubbles (one in Toronto, one in Edmonton), the listed “home” team went 59–71, a stunning 39.2 winning percentage. That was despite hockey being one of the few sports that grants strategic advantages to the home teams, which they retained in the bubbles. (Home teams have the ability to counter their opponent’s line changes as well as the small advantage of getting second stick placement on faceoffs conducted at center ice.) NHL teams have started the 2021 season by dominating at home, but that might even out à la the WNBA.

• In the English Premier League, there was no bubble. Home sides, playing in their own stadiums, won 41.6 percent and drew 20.5 percent of matches during the stretch of 2020 when no fans were allowed into stadiums, a drop from winning 44.8 percent and drawing 25 percent with fans in the stands in the prior season. Visiting clubs also boosted their goal totals from 1.22 to 1.36 per game, according to researchers at Nielsen’s Gracenote.

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• Major League Baseball also played its regular season without a bubble, at teams’ home stadiums, and with actual fans replaced by cardboard cutouts. In MLB, where the home team gets the benefit of batting last, home-field advantage appeared even stronger than usual, as the Ringer’s Ben Lindbergh outlined. Home teams won 55.7 percent of their games, higher than the historical average of 54 percent and the highest mark in a single season since 2010. The final three rounds of the playoffs were played at neutral sites, too small a number of games (35) to draw any conclusions. But “home” teams won 54.3 percent of those games, going 19–16.

• In the NFL, a league that would never dream of playing in a bubble, home teams (some playing in front of a limited number of fans) went 127–128–1 in the regular season and 6–6 in the playoffs, the lowest winning percentage in league history. (The Bucs won the Super Bowl in their home stadium, but they weren’t technically the home team.) ESPN’s Bill Connelly cautions against making too much of it “because it doesn’t tell you how good the home team or visiting team was.” The NFL’s home edge, he says, was “definitely diminished,” but most analyses suggest it still existed. It was just tiny.

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• And in equally bubble-averse college football, home teams (some, again, playing in front of smaller-than-usual crowds) went 318–216, a roughly 60 percent win rate that falls roughly in line with the sport’s history. That’s despite the loss of hundreds of non-conference games that would frequently pit big road underdogs from non-power conferences against richer home teams that are effectively paying them to get destroyed.

All in all, pandemic sports appear to show a home-field advantage that is diminished but still real, and an advantage that’s more strongly diminished in environments that are truly neutral.

It’s hard to reach firm conclusions about why this is happening—and ideally, we won’t get several more years of pandemic sports to expand our data set. But what we’ve seen so far has been useful in helping to evaluate different explanations for home-field advantage.

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The broadest theory, and maybe the one with the most cultural cachet, is that crowd noise overwhelms visiting players. Teams lean hard into this one, urging their crowds to get loud. The Pittsburgh Steelers play Styx’s “Renegade” before their most important defensive possession, with the explicit goal of working the home crowd into a frenzy. The Seattle Seahawks hold their stadium’s record-breaking noise in such high regard that the team’s fans are universally known as its “12th Man.”

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The fans explanation seems logical and might be true in certain instances, but it hasn’t been proved out. The Scorecasting authors made a persuasive case against it when they pointed to various plays across sports that might leave individual athletes most vulnerable to yelling and taunts from opposing fans—NBA free throws, NHL shootout attempts, NFL kicks and punts—and found no significant differences at home or on the road. (However, whether it’s because of the fans’ hollering or other reasons, MLB hitters do fare better in their own ballparks.)

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The pandemic might offer some encouragement to those who think fans have a major impact on visiting players. The NBA’s leaguewide free-throw percentage in the bubble was 78.9 percent, an improvement on what was already tracking to be a record-breaking season. No fans screaming at visitors might have helped.

However, the NFL’s kicking stats don’t stick out from recent years. The league’s 84.6 percent made field goal rate is in line with general kicking improvements over the prior decade and isn’t close to the best mark ever. (That’s the 86.5 percent of field goals that kickers made in 2013.) The NHL bubble didn’t include shootout attempts because there are no shootouts in playoff hockey.

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Another popular rationale is that travel, or the lack thereof, gives the home side an edge over road-weary visitors. This one feels intuitive, but there’s, again, no empirical consensus. And it grows less intuitive with time, as professional and major college teams increasingly travel in style and rarely do so on the day of the game.

That the official “visiting” teams in the NHL and NBA bubbles performed so well compared with historical norms is a good sign for the travel theory. But the unusual hassle of traveling during a pandemic also makes comparisons challenging.

“During a pandemic, sleeping in your own bed versus sleeping in a hotel, I think, would potentially be significant in terms of performance,” Wertheim says now. “If you’re worried about avoiding a virus and you can get in your own car and go sleep in your own bed and not worry who’s pushing the elevator buttons in your hotel, I wonder if that might not account for a difference this year.”

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Yet another idea is that home teams are comfortable with their surroundings and derive some benefit from that familiarity. That could mean any number of things. Perhaps a baseball team’s grounds crew sets up the field to conform to the home team’s preferences. Perhaps a 3-point shooter benefits from a familiar line of sight. Perhaps cold weather is a huge problem for a football team that usually plays in a dome. (The pandemic hasn’t offered any special insight into the weather theory, but Scorecasting went a long way toward debunking it using weather data from thousands of games.)

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In support of the idea that environmental familiarity plays a role in home-field advantage is the fact that MLB hitters continued to fare better at home than on the road, suggesting a real level of comfort in their own stadiums. Meanwhile, along with their superior foul shooting numbers, NBA players posted an effective field goal percentage of 53.6 in the bubble. That was historically good, as the NBA has never posted a leaguewide figure better than 52.9 over a whole season.

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But was that really because every player in the NBA became more comfortable shooting in Orlando? It could have just been because NBA players are getting outrageously good at shooting, with the league’s nine best shooting seasons ever all coming over the past 10 years. This trend looks likely to continue in 2021, as the league’s effective field goal percentage is on track to be the best ever.

Another possible source of home-field advantage is that the rules sometimes prescribe advantages for home teams.

That only applies in a few sports, and the pandemic didn’t seem to reinforce these advantages. NHL teams were horrendous when at “home” in the bubble, even though “visitors” had to make substitutions first. (Conventional wisdom is that getting the last change is ultravaluable because a team can manipulate matchups to give its best scorers shifts against the other team’s weakest defensive groups.)

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Maybe the reason for NHL home teams’ bubble misery has more to do with another oft-cited driving factor behind home advantage: officiating bias.

In Scorecasting, Moskowitz and Wertheim make a compelling case that across sports, crowds psychologically influence referees into making favorable calls for the home team. This one also makes intuitive sense, and it hasn’t turned off data scientists who follow these things closely.

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“College basketball, I think, is probably the sport where home-field advantage matters most,” says Parker Fleming, an economist and college football writer who focuses on analytics. “But I think the mechanism there is largely [that] it’s loud, and 50–50 calls—which are very, very frequent in college basketball—go more for the home team. I think it’s less the environment is actually affecting play on the field, and more so it’s encouraging unconscious bias in the referees.”

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What did the pandemic reveal about this, the closest thing to a proven reason for home-field advantage? Well, it offered mixed signals.

The NHL bubble supported the idea, with road teams serving far less time in the penalty box than they had in prior postseasons. Something similar appears to have happened in MLB’s silent stadiums. Historically, home teams have enjoyed more favorable strike zones than have visiting teams, both on the mound and at the plate. That continued in 2020, but Baseball Prospectus’ Jonathan Judge found the discrepancy was less pronounced than it would be in a normal year. And in the English Premier League, Gracenote’s analysis found that visiting teams earned fewer yellow cards and more penalty kick opportunities when the stadiums were empty.

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Strong evidence that getting rid of crowds really did affect the refs’ favoritism, right? Well, maybe not. The Ringer’s Nora Princiotti found that in the NFL, penalty yardage margins between home and away teams barely changed in 2020, with visiting teams still losing a typical 3 net yards per game to flags.

“I think there’s data and there’s anecdote, and it feels really weird to have home games where the visitor can’t remember at halftime whether they’re home or away,” Wertheim says, “but I think we stand by our thesis that crowds impact officiating more than they impact performance.”

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On the hunt for home-field clues in the pandemic, college football seems like an interesting place to look, for a few reasons. First off, talking heads give game-day traditions and home crowds significant rhetorical weight, so the results in sterilized environments could be an especially interesting point of comparison. Second, college football’s pandemic season had more variables than other sports’. That meant different approaches to testing for COVID, different responses to positive tests, different crowd sizes in the stands, and different scheduling practices from conference to conference.

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But college football, in the end, might have told us nothing.

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For one thing, huge numbers of players missed games because of COVID protocols. (Conferences have not provided aggregate numbers, and neither has the NCAA, but programs frequently reported positive case counts and exposures numbering in the dozens.) That made the games anything but neat counterexamples for what happens in a regular season. Moreover, the actual results on the field sent mixed signals about home-field advantage.

The Big Ten and Pac-12 played abbreviated seasons without crowds present. In those leagues, home teams went a combined 38–43, a 46.9 percent win rate. Meanwhile, the SEC, ACC, and Big 12 had fans in the stands, up to around 25 percent of their stadiums’ capacity. In those leagues, home teams went 107–72 (59.8 percent). Maybe the fans made all the difference!

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Except—it’s not clear why that would’ve happened. In the three power conferences that put thousands of fans in their stadiums, visiting teams were penalized 1.6 yards more per game than home teams, not much different than the 1.8-yard margin nationally, among a mix of full and empty stadiums.

Yet another possibility: Maybe road teams in the Big Ten, Pac-12, and Group of Five conferences (which also had small or no crowds) benefited from relative silence, making it easier for them to run their offenses.

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But visiting teams in those conferences didn’t necessarily feel like they had it easier. Will Healy, the head coach at Conference USA’s Charlotte, says his 49ers were stunned by the silence at what’s normally a raucous stadium at Appalachian State. “It took even our guys a second to realize, ‘Look, we’re keeping score here, boys. This ain’t practice, and we’re gonna go up against somebody else that wants to beat us, and we gotta play our best to have a chance to win,’ ” he says. “And that’s kind of what the whole year felt like.”

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Beyond such testimonials, it might just be chance that home teams did better in conferences that were more amenable to putting fans in the stands. Fleming, the college football analytics writer, noted that the performance of home teams against the spread wasn’t materially different in 2020 than it was in the past several years (just under 50 percent covered) and any bounce in home teams’ win percentage might just be due to favorable scheduling.

After going through this exercise, might is the word that keeps coming to the foreground. The pandemic has given strong backing to the idea that there’s something at play in home-field advantage that goes beyond the noise generated by boisterous fans. But as to what that something is, the pandemic has provided data points for and against every explanation.

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Frenzied crowds, rulebook advantages, travel, environmental comfort, officiating bias. The truth is probably that a rotating but inconsistent mix of all of those different factors is combined to create a small but perceptible edge.

Pandemic sports have been a jarring spectacle, carried out on soundstages that bear little resemblance to the chaotic meccas where they are usually played. In many respects, they’ve existed in a separate reality from the one most of us have been inhabiting, where gathering even one time in a crowded space would be unthinkable.

There is little common ground between the recent experiences of sports teams and their public audiences, except for one thing: There is still value in the comforts of home.

Listen to an episode of Slate’s sports podcast Hang Up and Listen below, or subscribe to the show on Apple Podcasts, Overcast, Spotify, Stitcher, Google Play, or wherever you get your podcasts.

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