Mets rookie catcher nERD of -0.09 means a lineup full of d'Arnauds would score .09 runs a game less than a league average player over a 27-out game. However, that number is much improved from the beginning of the season.

So what is he doing differently? For one thing, d'Arnaud is standing a little bit closer to the plate, which, as this heat map from ESPN shows, has allowed him to cover the plate better since his recall.

Another interesting note is d'Arnaud's walk-rate has dropped since he was recalled from Las Vegas, but his strikeout rate has also declined, which means he's being more aggressive at the plate. As a result, his line drive percentage has increased from 18.0% to 22.4% in the second half, and his HR/FB rate has jumped from 9.5% to 12.5% since the All-Star break.

Usually, a higher walk rate is more desirable. But in d'Arnaud's case, a little less patience at the plate has allowed him to be less tentative.

There's still some work to do behind the plate defensively. So far this year, d'Arnaud has accounted for -14 Defensive Runs Saved, which is dead last among 19 qualified Major League catchers this season. But it's possible some of those defensive issues went hand-in-hand with early-season frustration at the plate, and it will be interesting to see if an improved offensive showing will help even out his defense a bit as well.

All in all, d'Arnaud's drastic second-half improvement is a welcome sight for the Mets, who hope to pair him with Lucas Duda, Dilson Herrera, David Wright, Daniel Murphy and Juan Lagares as position players around whom they can build around.