Take the field
Barça Femení are historically good — but will they win the UWCL again?
Welcome to the sixth edition of Plot the Ball for 2023.
After the return of the men’s competition in recent weeks, the UEFA Women’s Champions League is back tonight1. The current Barcelona outfit are a historically dominant team — but, in a sport as volatile as football, we shouldn’t overstate the probability that they will win it all for the second time in three seasons.
Barça Femení are historically good — but will they win the UWCL again?
As a rule, I try and steer clear of making predictions in this newsletter.
Doing it well requires a level of modelling expertise which I don’t possess — and, even done well, the amount of week-to-week uncertainty that is baked into professional sport means that it rarely gives you much more than a general steer in the right direction.
Over a large enough sample of contests — round-robin leagues, for example — (well) predicted and actual outcomes obviously begin to converge.
But a significant proportion of sporting contests aren’t repeated even a handful of times. In these cases, the comfort you might have that the best team or athlete will ultimately prevail goes out the window as a result.
To make matters worse, it just so happens that more emotional salience gets attributed to the sorts of contests which deal only in small samples, like single-elimination knockout tournaments.
And, as much as many fans want these high-leverage contests to be more revealing of a competitor’s ‘true’ ability, in reality they are just another data point to be used in assessing their level — and outcomes are driven more by randomness than most of us care to admit.
There are few places this is more clear than in the latter stages of the world’s major football competitions2 — as the coming months, which will see both the men’s and women’s Champions League titles decided for the 2022-23 season, will surely prove once again.
In fact, you could take all of the above as a long-winded warning against taking the opinions of anyone claiming to know how the remainder of the Champions League is going to play out too seriously.
You can quibble with the specific probabilities spat out by FiveThirtyEight’s predictive model — and City and Bayern being drawn against one another in the last eight complicates matters4 — but it’s fair to say that the aggregate probability that one of those two teams is the eventual winner is around the same as the chance of a flipped coin coming up heads5.
As a consequence of examples like these6, my general rule of thumb is: no matter how much your heart wants a team to progress all the way through multiple rounds of a knockout tournament — and no matter how good your head thinks they are — it’s almost always a good idea to bet on the field instead7.
There is probably only one team in world sport that currently causes me to question the utility of that rule — and they happen to be competing in the Women’s Champions League against AS Roma later this evening.
FC Barcelona Femení’s last two seasons of play have been astonishingly good: they won a pair of domestic leagues while scoring over 5 goals per game on average, as well as the club’s first UWCL title in May 2021.
And they’ve continued this form into 2022-23, despite the continued absence of two-time Ballon d’Or winner Alexia Putellas.
Even compared to the other UWCL quarter-finalists this year — who are themselves the top teams in their respective leagues — their domestic dominance is on another level.
Consider their net expected-goal (or xG8) difference — a measure of how many goals they’d expect to have scored based on the quality of the chances they’ve created, less the goals they’d expect to have conceded on the same basis.
Looking at how it has accumulated throughout this Liga F season — relative to the other surviving UWCL sides in their own leagues — paints a clear picture.
Adjusting for the fact they’ve played more league games than their peers makes little difference: their net xG difference per game of +3.2 dwarfs Lyon, who are in second place at +2.2 per game.
Some of this gap will undoubtedly be due to the relative strength of other European leagues; Barça Femení are the only Spanish team in the UWCL last eight, while two French, two English and two German clubs all qualified.
Nonetheless, you probably shouldn’t take too much air out of their domestic numbers.
They’ve been almost as good (+2.9 xG per game) in Champions league play over the last two seasons — and, again, the strongest of this year’s quarter-finalists by a significant distance.
All of this data would probably lead you to the conclusion that there’s a bigger gap between Barça Femení and their peers in the UWCL than between the top teams in the men’s bracket and the rest9 — and assume a higher probability of them winning the competition outright too.
But should you really favour them over the rest of the field by any meaningful margin?
All I will say is that you don’t have to look too far back in history to be reminded of the fact that even teams this dominant are prone to fairly random single-game outcomes.
Only a few months ago, they lost 3-1 to Bayern Munich in the UWCL group stage despite creating a comfortably superior set of chances to their opponent’s.
And as proof that even the best teams don’t always produce underlying performances at the top of their range, you can look to their defeat by the same scoreline in last year’s UWCL final against Lyon.
If the Women’s Champion League knockout rounds were structured as best-of-seven series — as in the playoffs of each major North American sports league — I’d feel much more comfortable predicting Barcelona’s name on the trophy this year.
But, of course, that’s not the case — and even two-legged ties, as UEFA favours, have their fair share of chaos baked in. Football, as the conventional wisdom has it, is a funny old game.
You can find the code for this piece on GitHub here
This post on FiveThirtyEight captures the reasons for this well: “Soccer is a tricky sport to model because there are so few goals scored in each match. The final scoreline will fairly often disagree with many people’s impressions of the quality of each team’s play, and the low-scoring nature of the sport will sometimes lead to prolonged periods of luck, where a team may be getting good results despite playing poorly (or vice versa).”
Unfortunately, FiveThirtyEight — whose work I’ve heavily relied on in this newsletter — don’t currently publish UWCL predictions.
Bayern’s probability of winning the UCL outright dropped from 25% in FiveThirtyEight’s 13 March forecast — after they had already qualified for the last eight, but before they knew their opponent — to 17% in their 20 March forecast after the draw. City’s current probability — post-qualification, and post-draw — is 29%.
If outcomes were completely random — and each of the last eight therefore had an equal probability of winning outright — their combined probability would be 2/8, or 25%.
See also: FiveThirtyEight’s predictive model for the NHL’s Stanley Cup playoffs, which — even accounting for multi-game series in each round — only gives the three best teams a combined 61% chance of winning the title.
The specific probabilities are obviously impacted by the nature of the specific sport you’re talking about — some are more prone to randomness than others — but I think it’s a good starting point nonetheless. Irish rugby fans — who, at this point can be fairly certain that their men’s team is the best in the world — might want to bear this in mind ahead of the World Cup later in the year.