NFL Connections #40, Answers
The full solution: all four groups and the 16 names, sorted from the easiest group to the trickiest.
2,000-yard rushing season
O.J. Simpson, Barry Sanders, Terrell Davis, Derrick Henry
5,000-yard passing season
Matthew Stafford, Jameis Winston, Ben Roethlisberger, Justin Herbert
1,800-yard receiving season
Calvin Johnson, Cooper Kupp, Antonio Brown, Julio Jones
20+ rushing TDs in a season
LaDainian Tomlinson, Priest Holmes, Shaun Alexander, Emmitt Smith