what other RBs in that system put up the same or even close to similar numbers as Davis? why didn't other teams just run the same ZBS and enjoy the same successes?
Portis was significantly better at the same point in their careers without a HOF QB.
Portis' 1st two seasons: 29 games, 3099 rushing yards, 3777 YFS, 31 TDs, 5.5 YPC, 8 fumbles
Davis' 1st two seasons: 30 games, 2655 rushing yards, 3332 YFS, 23 TDs, 4.6 YPC, 10 fumbles
However, when you take Portis out of that system, his numbers plummet:
Portis' 1st two seasons in Wash: 31 games, 2831 rushing yards, 3282 YFS, 18 TDs, 4.1 YPC, 8 fumbles