As you may have heard, defensive metrics have looked very favorably upon Adam Eaton thus far this season. Perhaps you've seen some tweets about it. Maybe you've heard it on the TV and radio broadcasts. Maybe you're really into stats and have looked them up yourself. In any case, Eaton's defense has graded out superlatively well.
So what does this all mean?
Why are his numbers so good?
A few reasons.
First of all, defensive metrics are partially a product of how many balls are hit a player's way. To score as well as Eaton has, you need to have a lot of opportunities, similar to how a hitter can rack up more value if he's given more plate appearances. If a lot of balls are hit in an outfielder's direction and runners are testing your throwing arm frequently, you're going to have a better chance to separate yourself from the pack. Both of those apply to Eaton.
Another reason lies in the design of both Ultimate Zone Rating and Defensive Runs Saved, the two most widely used advanced defensive statistics. The metrics do some things a little differently, but both effectively assume that there's areas on the field in which balls are converted into outs a high percentage of the time because a defensive player is generally stationed there. Other areas of the field -- between fielders, well behind them, far in front of them -- have much lower conversion rates. The trick is that the metrics don't incorporate exactly where the players are positioned on the field for a given play. Therefore, good or fortunate positioning can lead the metrics to think that a player is making some really tough plays when they actually aren't that hard given where he lined up. We've heard plenty about Eaton's good defensive positioning, along with the help that Austin Jackson and Daryl Boston have provided, so the narrative fits.
The third (and most important) reason is that yes, in addition to positioning and a fluky distribution of batted balls, Eaton has fielded extremely well. He's made no errors. Sure, he's had the benefit of 48 balls hit into his zone, which is second among right fielders to J.D. Martinez, but he's only failed to make the play on one of them. Furthermore, he's made 26 out-of-zone plays, the most of any right fielder. Some of that may be due to positioning. The rest is everything you've been seeing with your eyes, including good route running, acrobatic catches, and speed.
The outfield assists are important as well. Eaton leads all of baseball with six of them. As I mentioned above, runners are challenging Eaton's arm (likely because he's in a new position and coming off shoulder surgery), so that plays into it. However, it's much better if you gun down a runner than if you scare them into not running at all (though the latter is still valuable).
Here's a look at how much value outfield assists can provide. They're not all created equal, of course, but we'll review two of Eaton's big plays. If you don't want to bother with the details, you're in luck! I've isolated them with a nifty separate section in-between the star-divides.
No. 1: Eaton throws out Edwin Encarnacion at third base
Using Tom Tango's run expectancy matrices, we can estimate the amount of runs this play prevented. Had Encarnacion made it safely to third, the Blue Jays would have had a run expectancy of 1.130 for the remainder of the inning. Throwing him out drops it to .224, for a net gain to the White Sox of +.906 runs.
Eaton could have also generated value had the Blue Jays feared his arm and not run at all. If Encarnacion stayed at second base rather than running to third safely, the Jays' run expectancy would have dropped to .884, which would have saved +.246 runs for the White Sox.
No. 2: Andrelton Simmons gunned down at the plate
If Simmons scores here, the Angels get a run and are left in a situation (man on first, one out) with a .509 run expectancy. Instead, they get no run and are in a situation (man on first, two out) with a .224 run expectancy. Eaton's throw saves 1.285 runs.
Had Simmons received the stop sign, that would have saved the White Sox .379 runs versus the hypothetical situation in which he scores.
The runs saved don't go directly into Eaton's WAR. Eaton is measured against the average right fielder, and other right fielders sometimes make these plays, fail to make these plays, or don't get tested at all in these situations. It's the fact that Eaton's been able to convert on six such throws (more than anyone else) that's been the differentiating factor. Due to some combination of bad scouting and bad baserunning, teams have been giving Eaton more chances than they should and that has allowed him the opportunity to generate big value.
We should note that Eaton's aggregate defensive rating gets automatically taken down a peg due to the fact that he's playing right field rather than a more difficult defensive position (e.g. center field, shortstop, etc.). That his numbers are still so far ahead of everyone else's is a testament to just how much better he's been than the average right fielder.
For more details and fun memories, I highly recommend checking out August Fagerstrom's collection of Eaton videos from yesterday on FanGraphs.
Do these numbers mean Eaton is the best defensive player in baseball now that he's in right field?
No! Of course not.
Defensive metrics can be fickle from season to season, let alone from month to month. There's not enough data here to conclude something like that. You wouldn't say that a hitter that batted .400 for a month is the best hitter in the game. The same logic applies here.
Furthermore, defensive metrics aren't as concrete as something like batting average. You should always supplement information you get from the numbers with what your eyes see.
Alright, so the numbers aren't all that predictive. Is it fair to say he has been the best defensive player in baseball so far?
Maybe. I would argue "yes". But this is where things are admittedly ambiguous.
The first reason I'd put forth that Eaton "deserves" these defensive numbers is that they're consistent with the eye test. Everyone from fans to broadcasters to teammates are raving about the work he's done in right field. He's made spectacular grabs, has flashed excellent range for a corner man, and has generally played flawless defense. We can credit Jackson, Boston, and whoever else has had a hand with Eaton's positioning a little as well, but it takes one man to talk and another man to listen. Eaton's doing all the right things.
The second reason is that even though part of Eaton's numerical success is the product of opportunity, he's done everything he can to capitalize on that opportunity. Sure, his numbers aren't sustainable. Opponents are going to learn to stop running on him so much and he's going to eventually get a smaller distribution of batted balls hit his way. He'll probably ::gasp:: make an error or a bad read at some point. However, even if one thinks it won't continue, that doesn't change what's already happened. Eaton has converted six baserunners into outs and has effectively made every play a right fielder could realistically be expected to make, many of them difficult and in key situations. That has provided the White Sox with plenty of value, even if it's most likely not repeatable.
It's this defensive play that has Eaton ranked so highly on the WAR leaderboards. The pace he's setting won't last even if he continues to perform very well in right field. However, that shouldn't make you question the valuation of what he's done so far. The defensive component of WAR (either kind) sometimes misrepresents the truth, but that's not the case with Eaton. We've seen the numbers and we've seen his actual fielding. The value is real.