Methodology · Euro
How soccer luck is measured, and how well it holds up
The same question as for every league on the site: with the way both teams actually played, how often does each win a replay of the match in which every chance falls at its expected rate? In soccer almost all of that luck is in the shots: a 0.3 chance goes in three times in ten, and a season is decided by a few hundred of them.
How much better than the real table?
Halfway through a season, the luck-adjusted table predicts 25% more of how the second half goes than the real table does, and after ten matches 56% more.
| Matches | Real table | Luck-adjusted | Better by | Most |
|---|---|---|---|---|
| 5 | 15.9% | 32.6% | +105% | 72% |
| 10 | 30.8% | 48.1% | +56% | 71% |
| 19 | 38.8% | 48.6% | +25% | 67% |
Points per match in the real table against replay points, each over a team’s first matches, predicting its points per match over the rest of the season. Every measure tested.
The data
Every shot of every match with its expected goals (xG): the chance that a shot from that spot, in that way, goes in. The expected goals are StatsBomb’s, from their open data, which has every shot of whole tournaments and of one full league season: the World Cups of 2018 and 2022, the Euros of 2020 and 2024, and the 2015-16 Premier League and La Liga. They rate the chance, not the finisher. The open data has no current seasons, which is why the current ones on this site come from another source.
The model’s few fitted numbers (below) were fitted and tested on the same data: 1,517 league matches (the 2015-16 Premier League, La Liga, Serie A and Ligue 1) and 230 tournament matches. So the shot-based pages are measured on matches the model was tuned on; with so few numbers fitted that matters little, but the tests below are not out-of-sample for these seasons, and the page for a new season would be.
The replay with the same day’s form
Each team’s shots of the 90 minutes are resampled: as many as a Poisson draw around the number it took, each drawn from its own shots, each a goal at its expected-goals chance. Own goals come at the league’s rate (0.047 a team a match). 4,000 replays a match.
Score effects. A team that leads sits back and gives up chances it wouldn’t at level; a team that trails pushes. So a shot taken while protecting a lead stands for more of a team’s form and one taken while chasing for less: each counts 0.67 at −2, 0.82 at −1, 1.22 at +1, 1.49 at +2. Measured directly, the effect is confounded (better teams lead more often), so its size is the one that best predicts the rest of a season: after ten matches, r² 0.471 without it, 0.484 with it.
Calibration. The replay’s win, draw and loss chances match how matches ended: ranked probability score 0.150 against 0.228 for the league’s base rates. Holding out each league in turn, the best temperature on the other three is between 0.94 and 1.02, so the replay is used as it comes. Draws are a little underpredicted when one side dominates the chances (22% predicted, 27% drawn), as in every model with independent goals.
Luck shares
The narrowest view keeps every shot and redraws only its outcome. Should all of a team’s finishing above its expected goals count as luck? Some players finish better than the chances they get, but at team level it repeats only weakly. Coin-flip points with 75% of finishing counted as luck predict the rest of a season best after five and ten matches (half edges it after 19): 0.301 after 5, 0.477 after 10, 0.478 after 19, against 0.291, 0.453, 0.469 at 100%. Own goals are luck in full.
The adjust-the-assumptions panel
On each shot-based league match page the panel changes how much of finishing counts as luck, and flips a chance, then reruns the coin-flip replay of the 90 minutes in your browser (the same arithmetic as the engine’s, checked against it). The replay with the same day’s form doesn’t move: it resamples the shots as they were taken, so what you count as luck doesn’t enter it.
Knockout ties
A tournament’s group matches are replayed like league matches. A knockout tie replayed level after 90 minutes goes to extra time (a third of the 90 minutes’ scoring) and then to penalties, a coin flip; the number on the page is how often each side goes through. Its luck index is measured against who went through.
Win probability
The line on each match page is the chance of winning from the score and the minutes left, with goals for the rest of the match at the league’s rates (1.51 home and 1.13 away a match; the average at a tournament’s neutral grounds), a draw counted half.
Validation
For the seasons built from shots. What predicts the rest of a season: each measure over a team’s first matches against its points per match over the rest (r²), the four leagues pooled.
| Measure | After 5 | After 10 | After 19 |
|---|---|---|---|
| Actual points | 0.159 | 0.308 | 0.388 |
| Goal difference | 0.215 | 0.395 | 0.424 |
| Expected-goal difference | 0.279 | 0.451 | 0.464 |
| Replay points (the luck-adjusted table) | 0.326 | 0.481 | 0.486 |
| Coin-flip points, finishing as luck: 0% | 0.148 | 0.318 | 0.401 |
| Coin-flip points, finishing as luck: 50% | 0.279 | 0.448 | 0.480 |
| Coin-flip points, finishing as luck: 75% | 0.301 | 0.477 | 0.478 |
| Coin-flip points, finishing as luck: 100% | 0.291 | 0.453 | 0.469 |
| Most possible | 0.724 | 0.706 | 0.672 |
Calibration of the replay by bin (home win chance against home wins, league matches):
| Replay | Matches | Predicted | Won |
|---|---|---|---|
| 0% to 10% | 156 | 5.3% | 2.6% |
| 10% to 25% | 317 | 17.5% | 11.7% |
| 25% to 50% | 507 | 37.4% | 36.3% |
| 50% to 75% | 424 | 61.9% | 61.6% |
| 75% to 90% | 205 | 81.8% | 85.4% |
| 90% to 100% | 76 | 94.5% | 96.1% |
Known limits
- No betting line, so no “before kickoff” or “same teams, fresh game” number from a line.
- Red cards change a match, and the shot replay keeps the shots they produced but doesn’t replay the card itself.
- The shot model is fitted on 2015-16 seasons and four tournaments, the same matches shown on the shot-based pages; the game has changed a little since (more shots from closer in), which the expected goals carry, the shares less so.