NFL Connections #84, Answers
The full solution: all four groups and the 16 names, sorted from the easiest group to the trickiest.
1990s star QBs
Brett Favre, Steve Young, John Elway, Dan Marino
1990s star running backs
Barry Sanders, Emmitt Smith, Thurman Thomas, Terrell Davis
1990s star receivers
Jerry Rice, Cris Carter, Tim Brown, Herman Moore
1990s star defenders
Reggie White, Bruce Smith, Deion Sanders, Junior Seau