When we introduced Barrels as the first Statcast™ metric, we wanted to see who had the best combination of exit velocity and launch angle. That's the entire point of it, that a great batted ball needs both, because you can hit a ball 120 mph straight up and still not get a hit. That's why we defined it as batted balls that lead to a minimum of a .500 batting average and a 1.500 slugging percentage, though the average of all barrelled balls is more like .800 and 3.000 -- which is to say it's the absolute best thing a hitter can do.
As you'd expect, big sluggers lead the Barrels leaderboard. Last year, it was Jose Cabrera, Nelson Cruz and Mark Trumbo. In 2015, it was J.D. Martinez, Mike Trout and Chris Davis. But is there anything to be learned from the hitters who really started barreling in the second half, far outshining their first half? What happened to the hitters who did so in 2015?
That seemed easy enough to look up, so let's do exactly that. We looked at 268 hitters who had at least 100 plate appearances both before and after the 2016 All-Star break, and we generated a list of the biggest improvements in Barrels per batted ball (a better measure than Barrels per plate appearance, which penalizes those who draw walks). It's an interesting mix of names:
Biggest barrels per batted ball gainers, 2016 second half
+7.9 percent -- Evan Gattis
+7.2 percent -- John Jaso
+7.0 percent -- James Dozier
+6.8 percent -- Ryan Howard
+5.9 percent -- Hanley Ramirez
+5.4 percent -- Cabrera
+5.3 percent -- Joc Pederson
+4.9 percent -- Freddie Freeman
+4.8 percent -- Mark Teixeira
+4.6 percent -- Cameron Maybin

Let's focus on a few of those and see if we can figure out why, starting with Gattis, who turned a very slow .215/.281/.425 (85 wRC+) first half into a scorching .288/.358/.594 (153 wRC+) second half. It's easy to point to the February hernia surgery he had that erased just about all of his Spring Training and delayed his season debut until mid-April, and perhaps that played a role. But, as will be a recurring theme here due to the nature of the metric, being able to elevate the ball in the second half was huge. Gattis' ground-ball rate dropped from 47 percent before the break to just 34 percent after.
Ramirez is easy to explain, because he made a mechanical change in June that helped him elevate the ball, and he spent the rest of the year crushing, as we explained in detail in September. Dozier famously gets power because he pulls the ball in the air like no other righty, but it took him until June to get to it consistently in 2016, which explains his presence here.
Perhaps the most interesting name is Howard, an otherwise one-dimensional player who may have trouble finding a job for 2017, but can at least point to the fact that he very quietly hit .262/.324/.608 in the second half. That's indisputably great -- the best second half in Phillies history, depending on how you look at such things -- but part of the reason he's on this list is because his first half was so poor (.154/.214/.353) that any sort of improvement would have had a very low bar to clear.

So does this mean that we can assume these second-half gainers will maintain that performance in 2017? Not necessarily, because you can't just look at partial-season stats and exclude the data from the rest of the season, though you can weight it slightly more heavily due to the fact it's more recent info. But it's still useful to repeat this exercise for 2015, this time with the benefit of being able to see what they did in 2016.
In 2015, 286 hitters qualified by having 100 plate appearances in both halves. The five biggest second-half gainers were Chris Carter (+14.7 percent), Ryan Zimmerman (+11.6), Jungho Kang (+10.8), Marcell Ozuna (+9.2) and David Ortiz (+9.2).
Just by those five names, we'll call it an 80 percent success rate. Carter hit 41 homers and was basically a comparable hitter to Trumbo, though he remains inexplicably unsigned, while Ozuna had a standout first half and started the All-Star Game before struggling with injuries afterward, and Ortiz put up one of his finest seasons of a great career. Kang also crushed (.255/.354/.513, 133 wRC+) around injuries, while Zimmerman had an extremely disappointing season despite quality exit velocity.
So while we'd caution against guaranteeing 2017 success based only on second-half barreling, it's also not something you can do by accident. (It's no coincidence that Trout has 125 Barrels over the past two years, while Billy Hamilton, for example, has three.) Hitting a Barrel is just about the best thing a hitter can do. Doing it a whole lot more, as these hitters did in the second half, can't be a bad thing.