Good football numbers are hard to come by. Teams keep their models in-house, the best public ones sit behind paywalls, and what's left for free is mostly box scores that don't care who you played. I started Held Out to fix that: ratings that adjust for the opponent, separate a quarterback from the team around him, and tell you how far to trust them.
The name is the one rule every model here follows. Held-out data is data a model never saw while it was built. Everything on the site is fitted on earlier seasons and graded on games it hadn't seen yet, and an idea that didn't help on those games didn't make it in.
It's all free, with no paywall and no account. Play-by-play, rosters, and schedules come from nflverse, whose participation data includes NFL Next Gen Stats and FTN Data (CC BY-SA 4.0). Kickoff weather comes from Open-Meteo (CC BY 4.0). To see how the ratings work, start with the methodology.