The Mariners have added Jarrod Dyson and Mitch Haniger to their outfield this offseason and they already had Leonys Martin. The Rays traded Drew Smyly for a group of prospects, which they insisted (to at least some extent) include Mallex Smith, and they already had Kevin Kiermaier. I think the Mariners and Rays made these trades because they thought high-end corner outfield defense was undervalued.


We know about things by comparing them to other things. We know (sort of) how fast we are going on the bus by looking out the window. What each of us believes to be “good food” is based on the other foods we have tasted. In baseball, we know how good players are by comparing them to their opponents and teammates. At some point, those doing the comparing deemed the statistics available for such comparing—wins, losses, RBI, ERA, saves, home runs, stolen bases—to be inadequate. Those doing the comparing realized that some statistics were based on arbitrary definitions and that many statistics ignored contextual factors.

To make better comparisons in order to better know how valuable a performance really was, some really smart people created better statistics. The culmination of this endeavor, as you all know, was Wins Above Replacement and/or Wins Above Replacement Player. The idea of these stats was that by giving all players the same denominator (replacement level), we could then compare all players by the numerator (wins created).

An important caveat when using WARP to understand a player’s value: Replacement level is a function of production from players performing in a given season and those players are a function of decisions made by coaches (lineups, rotations, etc.) and management (rosters). Consequently, how much better a player performs above replacement level is not only a reflection of his talents, but also a reflection of the players chosen for use by front offices and coaches.

With teams no longer lowering replacement level via racial discrimination and with teams now less likely to lower replacement level by overvaluing wins or RBI, the point of bringing this up for today’s purposes is to note that teams might be unintentionally lowering the replacement level because of their preconceived notions about positional value. For example, before teams were able to quantify pitch framing they likely set too low of a baseline for pitch framers, which would have made the best pitch framers more valuable back then than they would be now.

This is all to say that I think there's reason to believe that many teams are underrating corner-outfield defense. I think there's reason to believe that corner-outfield defense might be an inefficiency that can be exploited.


When I was a child, sports people on the radio or television would say that you build baseball teams with “defense up the middle and bats in the corners.”

I remember Michael Kay, broadcasting Yankees games on MSG in the late 90’s, occasionally saying something to the effect of “[Joe] Torre has said he likes to have a two center fielders, one for center field and one left field, given the size of Yankees Stadium’s left field.”

Given the fallibility of memory maybe it wasn’t Kay and maybe it wasn’t Torre, but this is a logic that has been discussed regarding larger corner outfields, from left field in Yankee Stadium and right field in Fenway Park to the entire Coors Field outfield and other ballparks in between. And this logic makes sense at first pass because a better defensive outfielder will have more opportunities in larger outfields than they would in smaller outfields.

With a closer look, though, there are some flaws or, more accurately, some areas where this logic is not being fully applied. First, while some corner outfields are larger than others, are they large enough to significantly alter the value of the player playing in that space? Second, this logic is usually applied to corner outfields with large fair territories, but should we not also apply this to corner outfields with large foul territories? Third, teams only play half their games at home. Fourth, and most importantly, range is not simply a function of the amount of ground a player can cover on high fly balls, which would be the relevant area covered for large outfield spaces.

Outfielders field many different types of batted balls; from liners and grounders they try to cut off down the line or in the gaps to lower hang-time fly balls. While having a speedier, rangier, and/or more efficient-at-route-running outfielder likely helps the most with the originally considered high fly balls, those other skills certainly save runs in all outfield spots in all stadiums. We can also apply this logic to outfield throwing arms, where it has been thought that arm strength is significantly more valuable in right field than the two other positions. (Alex Gordon showed us the value of a strong arm in left field, particularly when many other teams are using weak-armed players in that position).

This is all to say that the sluggers-in-the-corners logic could be flawed in that a) players provide value by both creating runs and preventing runs, and b) there are a lot of runs to be prevented in the corners.


Some things about Adam Eaton:

  • He had the 12th-highest WARP (6.4) among position players last season.
  • He is entering his age-28 season.
  • He has an extremely team-friendly contract: $4 million in 2017, $6 million in 2018, $8.4 million in 2019, and team options for $9.5 million and $10.5 million in 2020 and 2021, respectively.
  • Last year he played 121 games in right field, 48 games in center field, and one game in left field.

Clearly, Eaton was a very valuable player last year and his contract makes him especially valuable to teams. What's odd, though, is that while Eaton was also a valuable player in 2014 (3.0 WARP) and 2015 (4.6 WARP) when playing all of his games in center field, he was not as valuable as he was in 2016 when playing mostly an outfield corner.

How did Eaton become more valuable by playing a less premium position? The obvious guess would be that he became a much better hitter and/or baserunner to offset his move down the defensive ladder. This guess would be incorrect. Eaton’s batted runs above average (BRAA) were 11.5 in 2014, 15.1 in 2015, and 11.8 in 2016. Additionally, he produced 5.9 base running runs (BRR) each of the last two seasons.

While it may seem counterintuitive, Eaton was able to push his WARP into the superstar realm in 2016 by, according to fielding metrics (read: proceed with caution), going from being worth 2.1 FRAA in 145 games in center field in 2015 to being worth 29.1 FRAA in 2016. How did that happen? Is there something about Eaton’s skill set that allows him to cover more ground in a corner than in center or to be a better thrower in a corner than in center? That seems really unlikely. Did Eaton just become better defensively? Maybe, but 27 runs better? Probably not.

What's most likely is that while Eaton himself did not change a huge amount, the baseline he was being compared against changed. In other words, while Eaton was average defensively compared to the other center fielders teams chose to use, he was well above average compared to the other right fielders teams chose to use. So, yes, Eaton is a lot more valuable than a replacement-level right fielder because of his defense, but the takeaway should not be that Eaton is a majestic talent, but rather that teams are using really bad corner outfielders, at least defensively.

So what should teams do? Again proceeding with caution because of the relative uncertainty in some defensive metrics, teams should not trade all of their good prospects for corner outfield defensive stalwarts like Eaton, nor should they sign Jayson Heyward to a monster contract because of his great outfield defense. Why? Because Eaton was an above-average center fielder before he moved to a corner and because the cost of acquiring Eaton was much cheaper before he put up huge fielding numbers in a corner.

Instead, teams should probably be acquiring center fielders, even fringier ones, and moving them to corner spots to stop themselves from plugging in players there who can only hit. There is some precedent for this. The Royals thrived for a few years by playing insanely good outfield defense, particularly from Alex Gordon and Lorenzo Cain in the corners. The takeaway should not be “wow, these guys are great in the corners, I bet they could play a passable center field.” Rather, the takeaway is that there is a cheap advantage to be gained by acquiring players who do not fit a typical corner mold and playing them there. And this isn't anything new—preventing runs has always been as valuable as creating runs.

Now, this strategy is not fool proof and might not even be feasible. For starters, acquiring center fielders is expensive and the market may already have corrected itself. Second, not every center fielder just moves to a corner and is suddenly Adam Eaton; teams would have to pick the right players. Third, acquiring such players via free agency might be tricky because the players may not want to play in a corner.


Again, we don't know, but a lot of the information we are seeing is telling us that a) teams are using bad-fielding corner outfielders too frequently and b) teams are paying for good-fielding corner outfielders when they might be able to pay less for seemingly average center fielders to play corner outfield. If both of these things end up being true, then center fielders (in being good-fielding outfielders) are getting underrated because they are in even shorter supply than we thought and could save more runs in a corner than they would give back via decreased outfield production. Maybe this is what the Mariners and Rays were seeing when they traded for the players mentioned initially. Maybe it's just coincidence, but maybe not.