Are the Yankees’ outfielders trending downward defensively?

Yesterday, Matt Provenzano took a look at how the Yankees’ outfielders fared by the new Statcast metric, catch probability. You should read Matt's write-up and the catch probability introduction on MLB.com, but here's the short of it: every fly ball that is hit has a certain chance of being caught, based on the ball’s hang time and the distance between where the ball will land and the position of the fielder. Now, we can see how specific outfielders fare on batted balls with different catch probabilities.

The implications of this are exciting, and they allow us to continue to improve our understanding of defense. Metrics like UZR and DRS have been around for awhile and used extensively, but they are known to be imperfect. This new Statcast info gets us even closer to evaluating a defender's true ability.

Matt found out a few things about the Yankees defenders, namely that Brett Gardner and Jacoby Ellsbury are pretty solid, while newcomer Matt Holliday struggles in the field. Now, let's take a look at how the Yankees outfielders are trending in terms of defense, based on catch probability.

Catch probability breaks batted balls down into five categories, from one to five stars, with one-star plays being quite routine (but not certain), and five-star plays being extremely difficult (but not impossible). Here's the rate at which batted balls in each of those buckets were turned into outs, in 2015 and 2016 (data courtesy of Baseball Savant):

Using those probabilities, and the number of opportunities each fielder had to make different plays, we can calculate the number of plays a fielder was expected to make, and compare that total to how many he actually made. Whether that differential is positive or negative, and to what magnitude, should inform us of that fielder's defensive skill (note: I'm borrowing this technique from the wonderful Jeff Sullivan of FanGraphs, who also played around with the new Statcast data here).

So let's look at how many plays above or below expectation the Yankees outfielders made over the past two seasons, to see if they appear to be on any sort of trajectory:

As already mentioned, Gardner and Ellsbury look like pretty good fielders by catch probability, which matches their general reputations. Hicks is also considered to be a useful defender, and his numbers support that. Holliday, always known for his potent bat, sees his defensive numbers lag far behind.

What is concerning is that there does seem to be a downward trajectory. In 2015, both Ellsbury and Gardner appeared near the top of the league in terms of catch probability. Gardner recorded nine outs above expectation in 2015 in 160 plays, while Ellsbury impressively also made nine plays above expectation in limited playing time.

In 2016, that was down to five outs above expectation for Gardner, and four outs above expectation in 118 plays for Ellsbury. Hicks sees a similar decline from above-average to just very close to average in 2016. And Holliday, whom the Yankees intend to DH as much as possible, simply couldn’t make many plays at all in a small sample in the field last year.

These findings seem fairly natural given the career stages of the players involved. Ellsbury and Gardner are both in their early-to-mid 30s, and while they are declining from very high peaks as defensive outfielders, their skills do seem to be atrophying. Holliday will hopefully be rarely called upon to actually play the field, but if he does, it might not look too pretty. Hicks isn't old, but it's possible he's lost a step from his younger years.

What's exciting is that we have cool new numbers that help confirm some of our suspicions. It's our intuition that aging players like Ellsbury and Gardner are losing a step in the field, and we now have more data to support that intuition. And this is only the beginning of the kind of analysis that Statcast might yield, as even more data becomes available and those of us in the public better grasp how to use it. As time passes, there will hopefully be even more for us to glean about the Yankees, and about baseball at large.