The idea for this post came about from reports last week that the Yankees were considering flipping Brett Gardner and Curtis Granderson on defense, with Gardner taking over in center and Granderson shifting to left field. Of course, Granderson had his forearm broken by a J.A. Happ fastball yesterday, so now the decision has been made for the Yankees, as Gardner will start the season in center field. However, the Yankees will still have to decide what to do when Granderson returns from the DL in May, and they aren’t the only team looking at pairing a couple of center fielder in their outfield this year.

The Angels are shifting Mike Trout to left field because they’re going to give Peter Bourjos a chance to play regularly. The Indians are moving Michael Brantley to left field because they signed Michael Bourn. The A’s are going to use Chris Young all over the outfield because they have Coco Crisp already. In some cases — Trout and Bourjos, for instance — the defensive excellence of both means that there’s probably no wrong answer, as either could play center field and have it look like the right decision. But, in New York, the question was a little more interesting, as Gardner is generally considered to be a better defensive player, and flipping their positions was a consideration based upon improving the overall defensive quality of the Yankees outfield.

It makes sense, after all, to have your best defenders play where the ball is going to be hit the most often, but how much does it actually matter? What’s the magnitude of the difference between having Gardner in center and Granderson in left versus the alignment the Yankees have run out the last few years?

Let’s start off by saying that this isn’t a question we can answer with exact precision. We can make some informed comments based on the data that we do have, but we all know that defensive data isn’t perfect. But, we do have some information, and we can glean some idea of the scope of the impact with an optimal outfield alignment.

I started off by asking Jeff Zimmerman for some data on balls in play — excluding home runs — distributions for the last three years. Here’s essentially how the total breaks down for 2010 to 2012:

Left: 119,713 – 31%

Center: 147,305 – 39%

Right: 114,032 – 30%

Included in those numbers are ground balls and pop flies caught by an infielder, however, and we don’t really care about those data points when trying to talk about the overall opportunities for an outfielder. So, if we just focus on balls in the air that are fielded by an outfielder, the numbers break down like this:

Left: 53,054 – 29%

Center: 78,460 – 43%

Right: 52,823 – 29%

Given how strongly the pull effect is on ground balls, it shouldn’t be too surprising that balls in the air appear to skew slightly more towards the middle than the entire population of balls in play. There’s likely some bias in these numbers since center fielders tend to take charge on balls that multiple players could get to, and a ball is more likely to be tagged as being fielded in center if the center fielder catches it, but it’s not going to be large enough to erase the conclusion that center fielders do have more balls hit in their direction than corner outfielders. Not exactly a new finding, but it’s at least good to know that the data supports common knowledge here.

So, now that we have something approximating a distribution spread, we can note that this data suggests that the distribution of air balls to the outfield is something like 30/40/30. And, interestingly, this corresponds almost perfectly to the distribution of putouts as well. Last year, Major League center fielders made about 12,000 putouts, while right fielders and left fielders made just over 9,000 each. So, we have both the distribution of chances and the distribution of outfield putouts coming in at something close to 30/40/30.

With that distribution in mind, we can now at the overall number of opportunities and get a sense for how many more plays a CF might be involved in than a corner outfielder over the course of a full season. Last year, 184,179 batters came to the plate. If we remove all the walks, strikeouts, hit batters, and home runs, we’re left with 127,055 balls that were put in play in some fashion, or right around 70% of the total number of plays. Of that subset of plays, 45% were hit on the ground, leaving us with just under 70,000 balls hit in the air — either classified as a line drive or a fly ball — in 2012.

That’s 2,330 balls in the air per team per season, and 10% of those are infield flies, which leaves with almost exactly 2,100 balls hit in the air to the outfield per team per season. Applying the 30/40/30 distribution, that would make the average chances per outfield spot on a team per season look something like this:

Left Field: 630

Center Field: 840

Right Field: 630

200 more plays per season for a center fielder than a corner guy. That’s an average that can fluctuate based on a team’s strikeout and groundball rates, of course, but it’s a nice number to keep in mind in terms of a baseline. Just based on the distribution of batted balls, a center fielder is going to get one more ball hit his way each game than a corner outfielder. Clearly, playing your best defensive outfielder in center is a good idea.

But, at the same time, it also highlights that the magnitude of who plays where isn’t all that enormous. For one, these are season totals at the team level, and very few players play every inning of every season. Last year, the only outfielder to play 1,458 innings — 9 times 162 — was Adam Jones. Only Alex Gordon and Hunter Pence also cleared the 1,400 inning mark. The average innings spent in the OF for the 90 outfielders who played the outfield most often last year was 1,015 innings, or about 70% of the total innings available. Even if we limit it to the top 60 outfielders in terms of innings — assuming every team has two regular OFs who play most of the time — we come out to an average of 1,160 innings, or 80% of the available playing time.

So, unless you happen to have two iron man candidates in the outfield, they’re not going to experience the full effect of those 200 additional chances for the CF. Accounting for a realistic amount of playing time, moving a corner outfielder to CF will result in something like 150 to 175 additional balls in play hit in his general direction. But, of course, not all of those balls will be catchable.

Last year, the overall BABIP on balls in the air for MLB hitters was .336, meaning that 1/3 of those extra balls in play are likely to go for base hits no matter what kind of alignment a team is running out there. So, we’re already chopping 50 to 60 chances off the total opportunity difference, just based on the fact that many of those extra chances are simply fielding a screaming line drive that is going to hit the wall no matter who is chasing it.

Now, we’re left with something like an extra 100 to 115 catchable air balls for a center fielder over the course of a full season. But, just like there are non-catchable balls, that total also includes a large number of plays that any reasonable Major League outfielder will be able to make. The selection process for Major League outfielders weeds out the completely hopeless, leaving us with a spread of talent that isn’t all that large.

Of the 107 Major League outfielders who were given at least 500 innings last year, J.D. Martinez caught the fewer number of balls that BIS graded as being “in his zone”, coming in at 82.4%, and that’s dealing with a small sample of just 108 chances. Of outfielders who have played at least 1,500 innings over the last three season, Logan Morrison grades out with the lowest rate of catching balls in his zone, coming in at 84.7%. Essentially, even the most immobile outfielders get to something like 85% of all the balls that BIS thinks that they should be able to get to.

On the other side of the scale, the top-end OFs are in the 95% range. This isn’t exactly apples to apples, since a large part of being able to be a premium outfielder is to run down balls out of your zone, but it gives us an idea of the spread of talent between even great and terrible outfielders. Even the very worst Major League OF is going to catch a majority of those extra ~100ish balls that are hit in his direction and have some chance of being caught. And, of course, in each case that we talked about, we’re not dealing with the differences between a big range guy and a guy who should be spending a lot of time at DH. The spread in talent between guys like Gardner (caught 93% of balls in zone from 2010 to 2012) and Granderson (91% of same) is even smaller, as we’re dealing with differences between players who are already selected for having been among the better defensive OFs in the game.

What’s the exact number of extra plays that the Yankees might get from switching the two? Or that the Reds might get if they determine that Jay Bruce is rangier than Shin-Soo Choo? That requires more precise tools than we have available, but we can make a pretty good guess that we’re talking about a handful of extra outs per year. Maybe it’s a dozen if there’s a big gap in skills, as there might be with Gardner and Granderson now. But, overall, it’s not that big of a deal. There are a lot of balls hit to the corner outfield spots too, and defensive value isn’t simply constrained to up-the-middle positions. There are more balls hit to center, but once you factor in how many extra plays we’re talking about and the spread in talent between decent Major League outfielders, we’re not talking about a huge number of extra runs.

The main point is to get the right guys on the field; how you align them once they’re starting is more of a minor problem. Don’t worry too much about whether a center fielder is being wasted in a corner spot. There are a lot of chances to go around, and center fielders don’t get so many more meaningful chances that there’s a huge advantage to be gained by shuffling players between OF positions. There’s enough extra opportunities that your best guy should go in center field, but if it isn’t patently obvious who the best guy is, don’t stress about it too much. In the end, just put them side by side in some fashion and the results won’t be drastically different.