Play-level splits, opponent-adjusted ratings and availability tracking, each with the sample size behind it.
Ratings, tendencies and matchups. Offense and defense are solved together, not one against the other's raw baseline.
How a team plays with a player on the field — split play by play, so a game he left at halftime counts on both sides.
Who is actually going to be out there. Practice reports, reserve lists and a model for the ones listed questionable.