Data sources and terms

Where our stats come from, the terms each source sets, and how we keep to them.

Every Ledger Data table is built from nflverse's weekly player stats, which anyone may reuse under CC BY 4.0 as long as nflverse is credited. Each table and each CSV prints that credit. Each group of numbers is tagged with its source in our code, so a table can't be built from a source whose terms don't allow it. How each number is worked out is on the methodology page.

nflverse

Used in Ledger Data

Open NFL data built from the league’s play-by-play, updated every night in season. Its weekly player stats and its play-by-play (with nflfastR’s EPA, completion probability, expected YAC and expected pass rate on every snap) go back to 1999.

Terms: CC BY 4.0
How we use it: Every Ledger Data table and download, and the career, season and game-log pages. We add up and divide its weekly player stats and its plays ourselves, and fit our own expected-points model on its plays; the formulas are on the methodology page.
What we don't do: Nothing beyond its license: credit nflverse wherever the numbers go.
Credit line: Data: nflverse player stats and play-by-play, CC BY 4.0. Computed by Dynasty Ledger.

FTN charting, via nflverse

Not used yet

Play-by-play charting from FTN Data from 2022 on: first reads, catchable balls, play action and more.

Terms: CC BY-SA 4.0
How we use it: Not used yet. When charting stats arrive (first-read share is the first), they will sit in their own labelled section under CC BY-SA 4.0 with FTN’s credit, which means anyone may reuse those tables on the same terms.
What we don't do: Mixing FTN fields into one number with Next Gen Stats, Pro-Football-Reference or Sleeper data, which can’t be shared on those terms.
Credit line: Charting data: FTN Data via nflverse, CC BY-SA 4.0. Aggregated by Dynasty Ledger from play-level charting.

ffopportunity

Not used yet

An open expected-fantasy-points model and its weekly output, from the ffverse project.

Terms: CC BY-SA 4.0
How we use it: Not used. We may check our own expected points against it when those arrive.
What we don't do: Publishing it as our own model.
Credit line: Expected points: ffopportunity, CC BY-SA 4.0.

NFL Next Gen Stats

Not in Ledger Data

The NFL’s player-tracking stats: separation, time to throw, rushing yards over expected.

Terms: NFL terms of use
How we use it: A few figures on Scouting, credited to Next Gen Stats.
What we don't do: Tables and downloads. The NFL’s terms allow personal, non-commercial use and rule out building databases from it.

Pro-Football-Reference files in nflverse

Not in Ledger Data

Snap counts, advanced stats, the combine and the draft, which nflverse takes from Pro-Football-Reference.

Terms: Sports Reference data use policy
How we use it: Not in Ledger Data tables or downloads.
What we don't do: Republishing them in bulk. Sports Reference asks that its data not be used to build sites or databases that compete with its own.

Sleeper

Not in Ledger Data

The fantasy platform most of our users play on.

Terms: Sleeper terms of use
How we use it: League sync: your leagues, rosters, matchups and trades, through Sleeper’s API.
What we don't do: Ledger Data tables and downloads: none of them use Sleeper’s stats.