The Problem With Homefield Advantage

Why it might take a long time for Totteham Hotspur Stadium to become Tottenham Hotspur's stadium

Rejoice! There might not be the cheese room that was promised, but it’s finally happening: Tottenham Hotspur are moving into Tottenham Hotspur stadium, and they’re moving in tomorrow. Really! The project, it turns out, was not a false flag operation by chairman Daniel Levy to head-fake fans away from his continued transfer-market inactivity and player-wage suppression. The stadium was originally scheduled to open with a game against Liverpool on the weekend of September 15, 2018, but as Levy put it, there was a delay due to “contractors missing deadlines and possible future unforeseen issues”. They’ve staged two prep games in the stadium already -- a 3-1 win for the under-18 team against Southampton, a 4-3 loss for Spurs Legends against Inter Forever -- and honestly, I’m only writing this sentence so I can use it as an excuse to post highlights of that time Gareth Bale went to Italy and temporarily channeled the spirit of the Welsh mythological figure known as Bendigeidfran.

Spurs head into their new ground in something of a tailspin, as they’ve won just one point from their last five Premier League games. They’re in fourth place, even with fifth-place Manchester United on points (but ahead on goal differential) and just one point clear of Chelsea in sixth. Oh, and they still have to play Manchester City ... in Manchester. However, two potential reasons for optimism: First, despite a crushing, frankly unbelievable, and (depending on your worldview) perhaps hilarious own goal to hand Liverpool a 2-1 victory on Sunday, Tottenham played the table-toppers toe-to-toe: expected goals, total passes, passes in the attacking third, passes into the penalty area -- it was all relatively even. And no. 2: They play five of their last seven games at home.

Except, in the race for the Champions League places, Tottenham doesn’t quite have the clear edge. In fact, it might take years for their home-field advantage to finally kick in.

Back it up for a second, buddy. Why does home-field advantage exist in the first place?

No, no. You back up for a second, buddy. Who are you?

I’m the worst person you see in the mirror, I’m your unconscious, I’m the wild being trapped inside of all of us.

Uh … what?

Just kidding. I’m a now-meta structural conceit you’re employing to tell this story. So, get on with it!

OK! In their book Scorecasting, Jon Wertheim and Tobias Moskowitz boiled the explanation down to this: a few parts travel and a lot parts referee bias. Plenty of studies have found that referees make various decisions that favor the home team. They add extra injury time on to matches when the home team is losing and do the opposite when they’re winning. They award more yellow and red cards to away players than their opponents. And they give the hosts more penalties than the visitors. Here’s the split from the past six Premier League seasons:

There’s also some strange, conflicting research about the differences in testosterone and cortisol levels in male players’ bodies when they play home vs. away, so maybe the HOW-HYPE-YOU-GET FACTOR has an effect, too. Or, maybe it doesn’t.

Whatever the exact reasons, professor David Spiegelhalter found that the results across most leagues hover around these proportions: 48 percent home wins, 26 percent draws, 26 percent away wins. So far this Premier League season, 380 matches have been played: 48 percent have been home wins, 33 percent away wins, and 18 percent draws. In Italy the split is 43/28/29. In Germany it’s 45/24/31. In Spain, it’s 41/30/29. And in France, it’s 42/29/29.

Have you seen highlights from back when Pele was playing? Please watch them before you answer my follow-up question.

The game’s changed, man. Has it always been this way?

No! Over time, homefield advantage has actually declined. Back before the turn of the 20th century in England, home teams would win around 60 percent of games, while the other 40 percent were split evenly between road wins and draws. Blame it on postmodernity -- luxury travel, sky-rocketing ticket prices, ease of watching on TV, a shift in fan focus from team to player, eroding community institutions -- and you might be wrong. The same changes have hit other pro sports, and none of them have experienced as drastic of a decline, or any decline at all re: home wins.

The best explanation? A drop in goal scoring. From FiveThirtyEight:

Although scoring for either side has fluctuated, visitor goals have remained relatively constant, floating mostly between 1.00 and 1.3 per game. Home goals have fallen to roughly 1.5 per game from more than 2.5. The average difference (home goals minus away goals) has fallen to about 0.3 goals last year from about 1.1 goals at the league’s founding.

Goal-scoring on the whole started to decline in the 50’s but leveled off and has remained relatively constant since the 80’s. From the book The Numbers Game:

Turns out that most of that decline specifically comes from a decline in goals scored by the home team. I’m at a loss for why that might be -- my initial thought was that road teams might’ve started to play more conservatively with the accumulated knowledge that they kept getting tonked when they played away from home, but that would seem to be contradicted by the fact that they’re, you know, still scoring the same number of goals. Maybe it’s because the quality of the fields and stadiums have improved, so there’s less of an advantage to knowing how the ball moves on your home turf and catering your playing style to it? I’m all ears for other theories.

OK, so what does this mean for Tottenham?

Well, home-field advantage has never been less important, so there’s that. But the bigger issue is that, historically, moving into a new stadium makes the home-field-advantage effect even weaker. Mark Taylor, an analyst who has worked with Premier League teams, wrote about this back in 2012 and recently updated his analysis for Tottenham’s pending move. Before Spurs, 29 other Premier League teams had moved to new stadiums since 1990, and, as Taylor writes:

The final season in their old ground does see an upturn in performance relative to their road trips that is over and above league expectation, which may indicate a desire to give the retiring ground a rousing send off.

Once our sides have made their move there is a noticeable decline in home field advantage in the initial season. As a group, new tenants have a home field advantage that is just 88% of the prevailing HFA of their peers at the time of their move.

This depressed home advantage then gradually returns to league wide levels over the next three or four seasons.

In the final season before teams moved out of their stadium, they performed 22 percent better than league average at home compared to away, but then in the first season in the new ground, they performed 12 percent worse, then eight percent below average the following year, and five percent the year after that.

There is, of course, a complicating factor for Tottenham’s case: They left their home nearly two years ago. Spurs stopped playing in the intimate, 36,000-seat White Hart Lane at the end of the 2016-17 season. In keeping with Taylor’s research, Mauricio Pochettino’s side had the best home record in the league that season, winning 17, drawing two, and losing none for 53 of a possible 57 points while scoring 47 goals and allowing just nine. They then spent all of last season and most of this year in the cavernous temporary hinterland that is the 90,000-seat Wembley stadium. There was no send-off excitement at Wembley because it was never Tottenham’s stadium, and there was also no real acclimation with Wembley since it was ... never Tottenham’s stadium. Tottenham have been the sixth-best home team and second-best road team both this season and last season.

I asked Taylor what effect this weird transition might have on the club’s home performances, and he said, “They're unique in that respect, but I'd guess they'll pretty much follow historical precedent and be more likely to see a slight drop off in home form relative to what you'd expect from their away performances.”

Well, tell me who’s gonna win -- er, finish in third and fourth.

OK, OK. So here’s what—just kidding. I’m not gonna do that! There are three points between third and sixth; there are seven games left; each team is averaging somewhere between 2.03 and 1.94 points per game. Anyone who can predict that outcome with certainty is a god, a shaman, or a scallywag. To me, Arsenal and Tottenham are still the favorites to finish third and fourth because they’re, well, they’re currently in third and fourth. But I also think they’re both particularly tough to project. Whatever the effect of Tottenham Hotspur Stadium ends up being, history at least suggests that Tottenham won’t get the same kind of homefield boost that their competitors do. That’s a disadvantage, considering that they have five home games left.

Meanwhile, Arsenal are clicking their heels together and whispering quietly to themselves whenever they hit the road. I don’t actually know what the right adverb to put here is, but let’s say “weirdly” -- weirdly, the home-and-away two-faced-ness has persisted despite a change in manager. Last season and this season, they/they’ve won the second-most points in the league at home. In Arsene Wenger’s last year, 2017-18, they were 11th on the road with four wins, four draws, and 11 losses on a minus-11 goal differential. And now, in Unai Emery’s first season with the team, they’re 10th, with five wins, four draws, and five losses on a minus-1 GD. Among Spurs, Manchester United, and Chelsea, the Gunners are the only team without a game remaining against a team from the top six. However! They have four road games against the teams in seventh through 10th place in the table.

Betting markets and FiveThirtyEight are pretty much in exact agreement: They project Arsenal to finish third with 76 points and Tottenham fourth 75. Bettors have United in fifth on 74, Chelsea in sixth on 73, while FiveThirtyEight flips it around. Wherever this goes, though, it seems like there’s a pretty good chance it’s still up in the air come the final weekend of the season. What happens then? Arsenal’s on the road, and Tottenham plays at home.