The NL Rookie of the Year debate will come down to defense

Baseball has some incredible rookies in 2018.

Between the likes of Ronald Acuña Jr., Juan Soto, Miguel Andujar, Shohei Ohtani, Walker Buehler and Shane Bieber, to the more under-the-radar types in Jack Flaherty, Harrison Bader, Joey Wendle and Brian Anderson, the 2018 season is shaping up to have one of the better rookie classes in recent memory.

It’s time to focus on the National League, where it appears that we have a two horse race between Acuña Jr. and Soto.

In these two, we have witnessed some of the best play in baseball by some of the youngest to play the game.

Soto, who is just 19, began this season with Class-A Hagerstown, before the Nationals promoted him to the majors in late May due to a myriad of injuries that decimated their lineup. Nobody expected Soto to put up the numbers that he did, and because he just would not stop hitting, he was never sent back down to the minors. Soto has set all sorts of records, and he is currently on pace to finish with the second-highest OPS+ (142) by a teenager since 1901. A strong finish and he may pass Whitey Lockman’s 146 mark, though that seems unlikely.

Acuña hasn’t received quite the same attention due to his age, because he is not a teenager. However, he’s not much older than Soto considering he played all of 2018 as a 20-year-old. His ascent to the Majors wasn’t quite as unexpected; Acuña reached as high as Triple-A in 2017, raking at every level. The Braves promoted him to the big leagues in late April (being held down likely due to service time reasons) and has been one of the best hitters since, helping the Atlanta Braves capture their first NL East crown since 2013.

The similarities between Soto and Acuña are striking. Both are primarily left fielders, both have a similar size and stature and both have put up the same offensive numbers. I kid you not, their offensive numbers are nearly identical.

When I meant nearly identical, I really did mean nearly identical. They both have different strengths; Acuña has more power, while Soto has better discipline. But, these strengths pretty much cancel each other out. That is, Acuña’s worse plate discipline is made up with his better power numbers and vice versa for Soto. That separates their wOBA values by just three single points and their wRC+ values by just one.

That makes voting for one or the other a much harder task. Obviously, one could just go the easy way and say, “Acuña was playing in a pennant race, making his better play more valuable,” but that’d be lazy and uninformed decision making. Unlike MVP voting — where this argument still shouldn’t be used but is anyway — we’re not picking which rookie was the most valuable. We’re picking which rookie was the best.

That makes their cases come down to base running and defense. Stolen bases — where Acuña has nearly three times as many as Soto — certainly favor the Braves’ youngin’. However, base running runs above average, which shows us how well a player took an extra base, tells a much different story. Acuña still has a slight lead, with 3.2 base running runs, but Soto isn’t that far behind, with 2.7. On top of that, FanGraphs uses base running runs as part of their offensive runs above average formula, which Soto leads by 0.5, as seen in the chart. So base running looks like a wash.

Thus, it comes down to defense. Defensive metrics rate neither Acuña nor Soto highly, considering them both slightly below-average fielders. Baseball Reference’s Total Zone Fielding Runs Above Average (Rtot/yr), says that Acuña has been worth -4 runs “above” average, while Soto has been worth -9. FanGraphs’ defensive runs above average mark tells a similar story: Acuña has posted -5.1 mark, while Soto has posted a -9.5 mark. Baseball Savant’s information agrees: Acuña has been worth +3 outs above average to Soto’s -5. Defensive runs saved favors Acuña the most, at +5 across the three outfield positions, versus Soto’s -5.

Baseball Prospectus’ defensive marks, however, show Soto having better defense. He has put up 2.3 Fielding Runs Above Average (FRAA), according to their calculations, versus Acuña’s -10.2.

Here’s all of that information broken down nicely in a chart:

Clearly, Acuña has been the better defender. It’s hard to argue that. But neither of them have been great defensively. I have a tough time giving a player an award because he was “less worse” at playing his position than another. Alas, considering their offensive numbers are so close, it’s probably the best way to settle this. It’s certainly better than just handing Acuña the award because the Braves were in the postseason hunt.

Regardless, it is going to come down to the voters, who really aren’t presented with a bad choice. Whether Ronald Acuña Jr. wins the award because of his defense, or Juan Soto does because of the uniqueness of seeing a teenager in the big leagues, it really does not matter. Both of these players are well on their way to having extremely successful Major League Baseball careers.

Devan Fink is a Featured Writer for Beyond The Box Score. You can follow him on Twitter @DevanFink.