Fixture difficulty ratings are everywhere now. A grid of upcoming matches, colour-coded green through red, telling you which teams have a favourable run coming up. They're used for fantasy football, for previews, for assessing whether a struggling team is about to climb.
The presentation implies a model. Usually there isn't much of one.
What most of them actually do
The typical implementation ranks opponents by current league position, or by a simple rating derived from recent results, and assigns a colour band.
That's it. Playing the team in second is red, playing the team in eighteenth is green, with some adjustment for home or away.
The problems with that are immediate. League position early in a season is noisy. League position reflects results, which reflect luck as well as quality. And a single number ignores everything about the matchup.
The stylistic blindness
The biggest issue. Difficulty isn't a property of an opponent, it's a property of a pairing.
A team that struggles against a high press finds every pressing opponent difficult, regardless of where those opponents sit in the table. A team that defends crosses poorly finds every crossing team difficult. A possession side finds a well-organised low block harder than the block's league position suggests.
So a fixture list showing three green matches might contain the three specific opponents whose style causes this team the most trouble. The rating has no way to know that.
Building style-adjusted difficulty is entirely possible with available data — you can characterise teams by playing style and estimate matchup effects. Almost nobody does it in public tools, because it's more work and harder to display.
The static-rating problem
Most published fixture charts show the next five or six matches with ratings fixed at the time of publication.
But teams change. A side that's just appointed a new manager, or got its best players back from injury, or sold a key player in January, is not the team its rating describes. And the further ahead the fixture, the more likely the rating is stale.
Ratings six weeks out are essentially guesses about what a team will look like six weeks from now, presented with the same visual confidence as tomorrow's fixture.
The congestion blindness
A fixture chart typically shows opponents and venues. What it rarely shows is spacing.
Three matches against mid-table opposition in eight days is harder than three against the same teams spread over three weeks. A midweek European trip followed by a Saturday lunchtime kick-off away from home is materially harder than the ratings suggest.
Rest days and travel are among the more reliably predictive scheduling factors and they're absent from nearly every fixture difficulty tool I've seen.
The circularity
A more subtle problem with ratings based on current form or position: they're partly determined by the fixtures already played.
A team that's had an easy opening run sits higher in the table, and therefore appears as a harder fixture, than its actual quality warrants. The rating is measuring their schedule as much as their strength.
Ratings based on longer-run underlying performance are much more robust to this, and they're less common because they're less responsive, which makes them look wrong to users who expect the chart to reflect recent narrative.
What a better version looks like
If I were building one, the inputs would be: a rating based on chance quality created and conceded over a long window rather than results; adjustment for home or away with a modern, league-specific home advantage figure; days of rest before the fixture; travel distance; and a matchup adjustment based on stylistic profiles.
That's all computable from publicly available data. It would produce a chart that disagreed noticeably with the standard ones, particularly for teams whose results and underlying performance have diverged.
The reason it doesn't exist widely is partly effort and partly that the simple version is good enough for its main use case, which is fantasy football, where being roughly right is usually sufficient.
How to use the ones that exist
There is also a self-defeating quality to the popular ones that deserves mention. When a large number of people use the same fixture difficulty tool to make the same decisions, the advantage it might have offered disappears, because everybody has acted on it already.
This is most visible in fantasy football, where a well-publicised green run produces a wave of transfers into that team's players, which means the ownership is high and the differential value is gone before the fixtures arrive. The people who benefit are the ones who identified the run a fortnight earlier, usually by reasoning about it themselves rather than waiting for a chart to colour it in.
Treat them as a starting point rather than an answer.
Check the opponents individually rather than accepting the colours. A red fixture against a team whose underlying numbers are much worse than their league position is not actually a red fixture.
Look at the spacing yourself. The chart won't tell you that four of the six matches are in eleven days.
And be sceptical of anything more than about three fixtures out, where the ratings are describing teams that may not exist by the time the match arrives.
Used that way they're a reasonable convenience. Used as presented, they'll mislead you a few times a season, usually at the moment you're relying on them most.