According to reports, Kevin Kiermaieris on the verge of signing an extension that will keep him with Tampa Bay for the next six seasons, and you already know why, because you've seen him play. Based on both the data and the eye test, he's one of the most elite defenders in baseball. Kiermaier was winning Minor League defensive awards as far back as 2013; he's won Gold Glove Awards in each of the past two seasons; and he holds the mark (dating back to 2002) for the highest Defensive Runs Saved total on record, with 2015's +42 runs.
Within the Statcast™ laboratory, we've put a good deal of work into envisioning new ways to calculate outfield defensive skill, and we introduced our first version of that earlier this month, with "Catch Probability." You can, and should, read the full introduction, but the short version is that for every tracked batted ball, we can calculate how far the outfielder had to go and how much time he had to get there, and use the combination of those two numbers to judge the likelihood of the play being made, from zero percent (virtually never caught) to 100 percent (nearly always caught). As the year progresses, we'll improve to incorporate direction and wall balls.

As you might expect, Kiermaier ranks extremely well in this new metric, and we'll get to that in a second. But first allow us to point out that not only does it make him look good, he actually played a quiet role in how it was defined. Rather than using "hang time," which is the time from the ball hitting the bat, we're using "opportunity time," which is the time from the pitcher releasing the pitch. Why? Because Kiermaier (as well as other outfielders we've talked to) has said that he reads the catcher's signs to get a head start on the direction a ball is headed, and that's a skill worth noting.

Immediately, you can imagine the applications of this, but to start, we've assigned star ratings to each level of difficulty. That is, the most difficult catches to make, the ones that are successfully caught between zero percent and 25 of the time, are called "Five-Star Plays." Between 26 percent and 50 percent are "Four-Star Plays," and so on down the line. This has allowed us to do things like find Billy Hamilton's five most spectacular plays, for example.
So we looked at the 128 outfielders who had at least 100 potentially catchable balls in 2016, and we sorted them by who turned the most Five- and Four-Star opportunites into outs. Since those are all batted balls with a Catch Probability of 50 percent or less, that's another way of saying "Who was the best at turning balls that fell for hits more often than not into outs?" Guess who:
Highest conversion rate on balls with Catch Probability of 0-50 percent in 2016
65 percent -- Kiermaier, Tampa Bay
58 percent -- Desmond Jennings, Tampa Bay
55 percent -- Hamilton, Cincinnati
48 percent -- Jarrod Dyson, Kansas City
47 percent -- Keon Broxton, Milwaukee
42 percent -- Adam Eaton, Chicago White Sox
40 percent -- Travis Jankowski, San Diego
39 percent -- Jake Marisnick, Houston
38 percent -- Juan Lagares, New York Mets
38 percent -- Joey Rickard, Baltimore
Realize that the Major League average here was a mere 19 percent, and that eight outfielders in our sample, including Tampa Bay's Corey Dickerson, did not make a catch with a Probability below 50 percent. (Kiermaier made 17 such catches.) The surprise isn't that Kiermaier is atop this list so much as it is the gap he has over everyone else. (That ex-Ray Jennings, now with the Reds on a Minor League deal, appears so well is surprising, though he did have a +7 DRS, suggesting his fielding skills were still there.)

If we expanded this to Catch Probability plays of 75 percent and under (i.e. Three-Star Plays), Kiermaier leads there as well, converting 68 percent of his opportunities. If we just looked at all catchable plays, it's Kiermaier as well, turning 94 percent of the balls he had any chance of getting to into outs. The lowest-ranked fielders in our sample, Tyler Goeddel and Robbie Grossman, managed to get to only 71 percent. It's a huge gap.
Or consider what happened when Kiermaier didn't play last year, as he missed several weeks in the middle of the season after breaking his hand. Kiermaier started 102 games in center, with Jennings, Mikie Mathook, Brandon Guyer, Steven Souza Jr. and Jaff Decker covering the rest while he was injured or taking a day off. While we aren't controlling here for quality of pitcher, opponent, or pure luck, the difference in Tampa Bay's run prevention with and without him is stunning:
Tampa Bay's runs per game allowed with Kiermaier in 2016: 3.8
Tampa Bay's runs per game allowed without Kiermaier in 2016: 5.5
While there's evidence that defense isn't a skill that ages terribly well, Kiermaier is also only entering his age-27 season, and he is starting from such a high place that even a decline later in the contract might make him merely "acceptable" rather than "ridiculously good." He was also one of only eight outfielders to make a throw measured at 100 mph or more, according to Statcast™.
There's perhaps potential for more offense as well. Already a league-average hitter who hit 12 homers in just 105 games, Kiermaier doubled his walk rate from 2015 to '16, hit fewer grounders and began pulling more balls, all indicators of a hitter getting more comfortable at the plate -- and there's at least some evidence that Kiermaier faced more difficult pitchers than most hitters did.
But this is about defense, really. By the old stats or the new, the answer remains the same. Absolutely no one gets to more balls in the outfield than Kiermaier does -- and that's what the Rays are paying for.