Aaron Judge or Cody Bellinger?

There, atop the home-run leaderboard for the year, are two young stars on great teams in big media markets: Aaron Judge and Cody Bellinger. That’s a match made in heaven, at least for barside arguments around the country. Which one would you rather have?

The question itself is vague enough that the our first argument would have to be about the argument itself. Define your terms! Do you mean right now? Because if you mean right now, there’s little doubt that the large man in the Bronx is having the superior season.

Aaron Judge vs. Cody Bellinger
Aaron Judge 309 15.2% 29.8% 0.332 0.440 0.699 0.466 197 -0.5 36.5 0.1 4.7
Cody Bellinger 240 9.6% 28.8% 0.274 0.342 0.679 0.408 157 2.8 20.5 -3.3 2.5
Numbers entering play Monday.

Judge has the advantage in raw totals — which isn’t surprising, considering he’s also played more — but he’s also superior in the rate stats right now, both walking more often than Bellinger and offering greater defensive value so far.

It might be worth pointing out that Judge’s line is buoyed up by a .426 batting average on balls in play. There are a few modern ballplayers in the career leaders in BABIP (minimum 1000 plate appearances), but even the two at the very top — Miguel Sano (.365) and Mike Trout (.360) — are well below Judge’s current tally.

Andrew Perpetua’s xStats indicate that Judge’s combination of launch angle and exit velocity should have produced an .370 BABIP to date. So, even if Judge has been a little fortunate so far, he frequently makes hard contact in the good angles and should get more out of his balls in play than Bellinger (.325 xBABIP). Combined with the superior walk rate, that seems to tip the scales in his favor. And for xStats, it does: Judge has been 37% better than the league with the bat according to that metric; Bellinger, 30% better.

But that only addresses the present. Part of the allure of Judge and Bellinger is the promise each seems to possess for the future. And if we’re asking who we want in the future, we have another question on our hands — particularly if we ask some variant of “around which player would you rather build a team?” This is where their ages become more relevant — Bellinger is turning 22 this month, Judge just turned 25.

If there’s a flaw in either’s game that might be ironed out in the future, it’s the ability to make contact. So let’s consider the probability of each player improving in that area.

Look at how strikeout rate ages in today’s game, thanks to Jeff Zimmerman.

Today, your strikeout rate is likely to improve until you’re 25 and then get worse. Judge is already 25! What if he doesn’t improve his strikeout rate and Bellinger does? That aging curve suggests that Bellinger might be able to shave as much as two percentage points off of his strikeout rate by the time he turns 25.

In order to shave two percentage points off Bellinger’s current strikeout rate (before Monday’s game), we have to take either five strikeouts away (resulting in a 27.1% strikeout rate) or six strikeouts (resulting in a 26.7% strikeout rate). Let’s go with the latter. Now we can compare this fictional age-25 Bellinger — one who has just a 26.7% strikeout rate — to the current Judge using expected stats that normalize their balls in play based on comparable exit-velocity and launch-angle combos. More on how Perpetua calculates his stats is available here.

Real Aaron Judge vs Fake Cody Bellinger
Player K% xwOBA xwRC+
Real Aaron Judge 29.8% 0.441 189
Fake Cody Bellinger 26.7% 0.428 186
SOURCE: xStats.org
Fake Cody Bellinger is 25 years old and has cut his strikeout rate to 26.7%. xwRC+ derived in the comments using xOBA adjusted for league and park factor.

Judge still comes out on top, even after accounting for Bellinger’s potential improvement in strikeout rate. However! We’ve done this without applying similar age-related improvements both in walk rate or power to Bellinger’s line. Given generic aging curves, he should see more walks (until age 26), a little more power (until age 23), and better fielding numbers (until age 25). Add those up and you might get an equivalent line between the two of them.

There’s one last thing to point out that may be interesting to our debate, considering we’re trying to decide how they will age. Judge may be older than Bellinger in terms of the age of his body parts, but in terms of playing baseball in the big leagues, they’re of equal age. Is it possible that players who debut later peak later because they get to make some of those same league adjustments, just later on?

I asked Jeff Zimmerman to run two aging curves, which he does using the Delta Method. One would look at the relative year-to-year overall improvement of players who debuted at 22 or younger, and the other would look at players who debuted at 24 and older. Here are those aging curves:

There’s little evidence that late debuts show an aging curve shifted to the right, with a later peak. By this curve, this year and next year are likely to be Judge’s peak years, and Bellinger still has five years to get to his peak. There’s a suggestion then that Judge could decline faster, if he ages like other late debuts. Look how that gray line is consistently below the orange one in the later years.

And that’s the simple fact that may push some to pick the Dodgers’ first baseman: those three years of catchup that Bellinger has on Judge are very valuable. Even if it looks like just a couple ticks of strikeout rate, a few more walks, and maybe a little better work in the field, it will all add up.

Consider this, though: it might all add up… so that Cody Bellinger is about the same as we’re seeing from Aaron Judge, right now.

With a phone full of pictures of pitchers' fingers, strange beers, and his two toddler sons, Eno Sarris can be found at the ballpark or a brewery most days. Read him here, writing about the A's or Giants at The Athletic, or about beer at October. Follow him on Twitter @enosarris if you can handle the sandwiches and inanity.

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6 years ago

Awesome article. This is going to be a fun debate to have for the next several years.

Also, Zimmerman’s k rate aging curve graph is really illuminating! Kudos to him as well.