We're now four weeks into the NFL season, and the list looks a lot different than it did two weeks ago, as we've seen a few rookies getting more reps (and trust) from coaches. Last season, the Jets hit a home run in the draft along the defensive line, and it looks like they'll do it again this year.

Here are the parameters, same as always:

This is a measure for all games this season, not just last week.

Total snap count matters. Staying on the field is a measure of value.

Positional value matters, but overall performance and impact on the team matter more.

Relative value matters. I ask: Would this player be a starter on most teams or on a good team?

Here's my latest ranking of the top 15 rookies in the NFL.

1. Leonard Williams, DE, New York Jets

I don't think he has been as good as he will be, but Williams gets bonus points. Remember, this defense has been without arguably the best pure run defender in the league in Sheldon Richardson. Williams has had to step up, and the Jets are allowing 3.8 yards per carry, among the best run defenses in the league. He has played 200 snaps, and they've meant a lot to the Jets, who are off to a 3-1 start.

2. Marcus Mariota, QB, Tennessee Titans

He's coming off the first game where his mistakes (interceptions) really cost the Titans, so it'll be interesting to see how he bounces back. That said, Mariota has been everything you could hope for and more if you're a Titans fan, and he's just getting started. If the 8-2 TD-INT ratio stays anywhere near where it is, we'll be talking about a remarkable rookie year. But it's early . . .