It's good, obviously, for Major League hitters to get the ball in the air. In 2017, we saw 387 hitters put at least 100 balls in play, and 385 of them (99.5 percent) had better production* on balls hit in the air** than on the ground. Fly balls and line drives lead to more success than grounders.
* We'll define production with Weighted On-Base Average, or wOBA, a stat very similar to OBP, except it gives more credit for extra-base hits.
** We'll define "a ball hit in the air" as being higher than 10 degrees of launch angle. Every single home run, and 89 percent of extra-base hits, came at 10 degrees or higher.
Hitters like Justin Turner, J.D. Martinez, Daniel Murphy and Josh Donaldson turned themselves into stars by elevating the ball in the air. Last year, we saw hitters like Ryan Zimmerman, Yonder Alonso, Francisco Lindor and Jed Lowrieget the ball in the air more and find success doing it. We saw Chris Taylor turn his career around in part due to remaking his swing to try to get more elevation.
But who's next? Who could turn things around by hitting the ball hard in the air more? Remember, it's important to have both angle and velocity. If you hit the ball in the air without hitting it hard, it won't help you much. If you're already hitting the ball at a high angle and go further, it can hurt you; just ask Ryan Schimpf and Trevor Story.
If we'd done this exercise last year, we might have pointed out that unheralded St. Louis outfielder Tommy Pham had the highest exit velocity on balls hit at 10 degrees or higher in 2016. Pham, of course, went on to have one of 2017's biggest breakout seasons. We might have noted that Alex Avila was fourth on that list, and he lowered his ground-ball rate by 14 percentage points and upped his slugging by 74 points.
It's easier said than done, of course, and swing changes can affect contact rate. But this is the direction the sport is going for hitters. Who should be next?
Yandy Diaz, Indians
No hitter in baseball who put at least 100 balls in play hit more balls below 10 degrees of launch angle -- i.e., "not in the air" -- than Diaz, and he didn't have a strong season. He hit just .263/.352/.327. Diaz didn't hit a single home run, despite 179 plate appearances and a better-than-average strikeout rate. Even in the Minors, he'd never hit more than seven homers in a season.
You might think this makes Diaz a slap hitter, like Jarrod Dyson, yet the data says otherwise. Of those 387 hitters, only four had a better hard-hit rate than Diaz, who crushed the ball at 95 mph or higher a massive 50.8 percent of the time. (And two of those four were Aaron Judge and Joey Gallo.)

To simply look at Diaz, you know he's a massively strong man, and we know that the Indians have passed this data along. He slugged .219 before a first-half demotion, and .402 after, with a higher launch angle. It's not enough, but it's something. Watch out, 2018.
Eric Hosmer, free agent
Hosmer operates in the odd space between "I had a very good season that will lead to a huge contract, so why should I change?" and "There's so much more in there, probably." He was something of a ground-ball machine last year, hitting more balls on the ground than 95 percent of other batters, but because he's shown the ability to hit the ball hard, his production in the air is actually very good -- when he can get there.
On air balls, Hosmer's .632 wOBA was in the top 10 percent of our 387 hitters, ahead of Freddie Freeman, Bryce Harper or Charlie Blackmon. In 2016, his .605 wOBA was also in the top 10 percent, similar to Paul Goldschmidt, Michael Trout and Corey Seager. Hosmer mashes when he gets the ball off the ground, it's just rare that he can manage to do it for a sustained period.

Hosmer is not like Martinez or Taylor or Turner, players who were on the fringes of the big leagues and dedicated themselves to change. He doesn't need to be, and maybe he'll never do it. But you can see why, with his talent, everyone wants to see what it could look like. When Hosmer gets the ball in the air, it ends well for him.
Ian Desmond, Rockies
This is less about velocity and more about survival and circumstance. Desmond's first season in Colorado was an injury-plagued disappointment, as he hit just .274/.326/.375 with seven homers, and a big part of that was too many balls on the ground. Desmond was second only to Diaz in terms of the fewest batted balls hit above 10 degrees. That's fine for, say, Dee Gordon, but the entire point of playing in Coors Field is to hit in the air. If it doesn't go out, there's tons of real estate for the ball to evade a glove.
Desmond has always been something of a ground-ball hitter, of course, but 2017 was a new extreme; after having 41.2 percent of his batted balls above 10 degrees in 2015-16, it was just 32.6 percent in '17. Think that matters? Last season, Desmond hit .413 with a .775 slugging above 10 degrees … and .345 with a .374 slugging below. A hitter can't take advantage of that thin air on the ground.

Kennys Vargas, Twins
Take a look at the top performers on balls hit at 10 degrees or higher. You'll see a ton of slugging stars in the top dozen, like Judge, Martinez, Giancarlo Stanton, Gallo and Donaldson. Extend it to the top 25, and you'll see Goldschmidt, Pham and Gary Sanchez. These are big names, yet there at No. 16 sits Vargas, who had an essentially league-average .253/.314/.444 year as a first baseman and designated hitter for Minnesota. How?
It's partially due to contact, as Vargas' 29 percent strikeout rate was significantly higher than league average in 2017, but we've seen that high strikeouts are fine if they come with big power. If you expand that list to production on balls hit at 10 degrees or higher and also at 95 mph -- i.e., hard-hit balls in the air -- Vargas is fourth, behind the Rockies' Pat Valaika, A's rookie sensation Matt Olson and Stanton. Yet the 6-foot-5 Vargas, who owns the two longest Twins homers tracked by Statcast™, saw his percentage of batted balls above 10 degrees drop from 60.4 in 2016 (when he slugged .500) to 49.0 in '17 (when he slugged .444).

Quickly running out of chances in Minnesota, it's time for Vargas to go all-in on all-air.