There's an interesting trend here if you look at some of the best rookie performances:

• Zack Martin played left tackle last year at Notre Dame. But he's played guard all year in Dallas.

• Same story with Joel Bitonio, who played left tackle at Nevada. He's also moved inside to guard.

• Khalil Mack has a good all-around game, but has excelled more as a run-stopper than he has in the pass rush.

• Anthony Barr was a pure pass-rusher in college, but that's almost a secondary part of his game now.

Notice anything there? In each example, you have a case where the guy is providing value right away, but the high-end hope for what that player could become in terms of positioning hasn't been fully realized. It's not bad to get a really good guard in Round 1, but you certainly pay a really good left tackle more money. Same with a guy who can consistently apply pressure on the QB versus a guy who is a stalwart in the run game. (To be fair, Mack is rushing the passer. It's Barr who has made a more significant change, and one that diminishes his role as a "disruptor.")

To me, this shows why it can pay to draft players who aren't just great at a high-end skill area, but also offer a functional versatility.

That all said, here are the usual parameters:

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

• 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? Remember, I've hit reset on these players as far as future value; this is all about production.

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

1. Zack Martin, OG, Dallas Cowboys

The story of the season for Dallas has been the effectiveness of the offensive line. And what's remarkable about that unit is if you go through every game (and that's my Monday this year), you realize that Martin has been the most consistent player. He's been outstanding, probably a top-10 player at the position league-wide. And remember, this is a guy who could flip outside to tackle.