The bits everyone
gets wrong.
No jargon and nothing to buy. If you read only one, make it the last.
What xG actually measures
Expected goals in plain English — what the number is, what it is good for, and the three things people constantly get wrong about it.
Closing line value — the only honest scoreboard
Why profit is a terrible way to judge whether someone is any good at this, and what we publish instead.
Why a real edge still loses money
We replayed the model across full past seasons. It beat the closing price and it still lost. Here are the actual numbers and why this happens to everyone.
Where the bookmaker's margin goes
Add up the chances implied by a set of odds and you do not get 100%. The extra is the margin, and most of what looks like value is the margin in disguise.
How you check a model is not lying to you
Calibration and placebo testing — the two checks that separate a model which works from one that has memorised the past.
The exam we set ourselves, and failed
We thought we had an edge. We froze it, tested it on an unseen season, and watched it die. This is the most useful thing on this site.