Claude built a browser football game, then self-played thousands of games to tune it
MDawg74 · reddit · 2026-07-21
A developer says Claude built a browser football game and then tuned it by playing thousands of self-play matches against NFL baselines.
- The game, CHALK, is a free browser football game where the user acts as the coordinator and draws routes while the AI runs all 22 players.
- Claude wrote the entire game in one HTML file, without an engine or framework.
- The interesting part is the testing loop: Claude wrote a Playwright harness, ran thousands of headless plays, compared the stats to NFL averages, and traced bad numbers back to specific bugs.
- After fixing issues such as an offensive line blocking bug, the metrics moved close to NFL ranges, including sack rate, interception rate, and fumbles per drive.
- The author also used the AI-vs-AI demo itself as a regression test to catch freeze bugs.
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