Why We Built MicroLeague Sports Vol. 3

Why Sports Data Is Harder Than Most People Think Building believable cross-era simulations turned out to be less about the engine and more about the data underneath it. Here is what we learned. MicroLeague Dev Blog, Vol. 3 By Eddie Solar When we started building MicroLeague Sports, I assumed the simulation engine would be the hard part. The vision was ambitious enough to justify that assumption. Let fans ask whether the 1996 Bulls beat the 2017 Warriors. Whether the 1985 Bears could slow down Patrick Mahomes. Which Cowboys team was actually the greatest. Teaching software to play those games across eras felt like the mountain. I was wrong about which mountain it was. The engine is hard, but it is a solvable, bounded kind of hard. The data underneath it is a different animal. Like most developers approaching this for the first time, we figured sports data was largely a collection exercise: gather historical teams, player stats, schedules, and box scores, feed it to the model, done. That assumption fell apart almost immediately, and the reason it fell apart is the subject of this article. Sports data is not a collection problem. It is an identity problem. Franchises do not stay the same thing. Players are not one entity. And the historical record does not agree with itself. The Real Problem Is Modeling Identity Over Time Volume 2 covered the era problem: statistics are confounded by the conditions that produced them, so a raw number pulled across decades lies to you. That is a normalization challenge, and it is real. But normalization assumes you already know what you are normalizing. Before you can compare the 1992 Cowboys to the 2023 Chiefs, your system has to have a confident answer to a more basic question: what exactly is a "team," and what exactly is a "player," when your dataset spans a hundred years? Those sound like trivial questions. They are not. They are the questions that ate most of our early engineering time, and getting them wrong quietly corrupts ever