Some have said it's relatively easy to start for the Rams when they gutted the team in the offseason. But the 4 guys you mentioned are performing as well as almost any rookie in the league, especially impressive when you consider that they were drafted in the 2nd, 3rd, 3rd, and 5th rounds. And I would add Ethan Evans (7th round) to that list.
The jury is still out on the rest of this draft class (Bennett, Hampton, McClendon, Allen, Tomlinson, Mathis, Z. Evans, Taylor, Johnson) but the Rams could end up with a couple more starters and a few rotational guys from this draft class before all is said and done.
AlbaNY_Ram
