So far, much of what we've reported with Statcast™ data has been about observing -- how fast was this, how high was that, etc. That's all going to lead to exciting new metrics to come out of the Statcast™ lab, and today we can share the first of many to come. Let's keep it simple: Let's use exit velocity and launch angle as a pair to find the hitters who just mash the most. 
Think about the best thing a Major League hitter can hope to do when he steps to the plate. He obviously wants to hit the ball hard, because the .626 batting average Major League Baseball has on balls hit 100 mph or more in the Statcast™ era is pretty compelling. He wants to hit it at the right angle, too, because a ball hit straight up or down isn't going to be a hit no matter how hard it's struck. What he wants to do is hit it hard at an optimal level for success. In the parlance of baseball, he wants to barrel the ball.
For the players themselves, that might be a "you know it when it happens" sort of feeling, but we can do a lot better than that. We can come up with the right combination of velocity and angle to identify those high-value batted balls, and from there, it's easy enough to make leaderboards that show the best hitters at creating them and the best pitchers at preventing them. Let's do exactly that, and let's name those optimally hit balls Barrels.
A "barrel" is defined as a well-struck ball where the combination of exit velocity and launch angle generally leads to a minimum .500 batting average and 1.500 slugging percentage, though it will require a bit more explanation than that. Perhaps the best way to show what kind of batted ball qualifies as a barrel is with this image -- the "Barrel Zone" is where barrels live:

As you can see, the "Barrel Zone" is an area that begins at 98 mph between 26 degrees and 30 degrees, and expands outward from there. The higher the speed of the ball, the wider the range of launch angle exists for a ball to be considered a barrel. At 99 mph and up, for example, between 25 degrees and 31 degrees is "barrelled." At 100 mph and above, batted balls between 24 and 33 degrees will always be considered a barrel, and so on, expanding as balls get hit harder. Those aren't arbitrary definitions; that's based on a review of all of those batted-ball types and outlining the area where you get your minimum of ".500 batting average and 1.500 slugging percentage."
If you look at the slugging percentage on all combinations of batted-ball velocities and launch angles, you can very clearly see the barrel zone appear in the upper right -- that's where crushed baseballs are. The lighter colored line extending below it also includes some extra-base hits, but mostly the kind of doubles and triples that are bloops, well-placed or generated by speed, which don't fit the skill we're looking for.

It's worth noting that most barreled balls have performance numbers much higher than that minimum. The overall average of any barreled ball yields a batting average of over .800 and a slugging percentage of nearly 3.000, which are extraordinary numbers. Think of it like the quality start, which requires at least six innings and no more than three earned runs, numbers that come out to a 4.50 ERA. Of course, most starts that qualify as "quality" are much better than that, and so the average ERA for all "quality starts" is actually under 2.00. 
So how often do hitters manage to do this? Perhaps less than you think, and that's what makes it special. The best hitters in baseball, as you'll see on our leaderboard, manage to barrel up the ball about 10 percent of the time they step to the plate. Across Major League Baseball, the ball is barrelled up in approximately five percent of all plate appearances. That number rises to seven percent if you consider only plate appearances that end with a ball in play, excluding walks, strikeouts and so on.
When you look at baseball's best at barreling the ball up -- and you can see a live leaderboard here -- you'll see some names you expect, but there's also a few surprises. Through games of Wednesday, baseball's barrel leaders are Mark Trumbo and Miguel Cabrera, tied with 63 apiece. Names like Mike Trout and David Ortiz also populate the top 10, which is all as expected. At the other end of the scale, Billy Hamilton has just a single barrel this year, which is a good reminder that while most home runs are barrelled, not all are. 
But while raw totals are interesting, that's also based on opportunities. What if we just looked at percentage of barrels per ball in play? We have 263 hitters with 200 balls in play so far, and look who's at the top.
Percentage of barrels per ball in play, 2016 hitters, minimum 200 balls in play
1. 18.4 percent -- Khris Davis
2. 18.3 percent -- Chris Davis
3. 17.6 percent -- (tie) Trumbo/Giancarlo Stanton
5. 17.3 percent -- Chris Carter
6. 16.9 percent -- Nelson Cruz
7. 16.0 percent -- Trout
8. 15.7 percent -- Ortiz
9. 15.3 percent -- Cabrera
10. 15.0 percent -- Mike Napoli
Gif: Khris Davis hits homer
If we'd lowered the minimum to only 100 batted balls, the leader would be Gary Sánchez, at 21 percent.
Of course, simply looking at performance on balls in play ignores the elephant in the room for many of those sluggers, which is that they often have difficulty putting the ball in play in the first place. So let's account for that issue by looking at who does the best at getting a barrel on all plate appearances, including strikeouts, walks, etc.
Percentage of barrels per plate appearance, 2016 hitters, minimum 200 balls in play
1. 10.8 percent -- Khris Davis
2. 10.1 percent -- Trumbo
3. 10.0 percent -- Cabrera
4. 9.9 percent -- Ortiz
5. 9.6 percent -- Cruz
6. 9.2 percent -- Stanton
7. 8.8 percent -- Trout
8. 8.6 percent -- (tie) Evan Longoria /Nick Castellanos
10. 8.5 percent -- (tie) Chris Davis/Carter/J.D. Martinez
Oakland's Davis doesn't usually get brought up when we talk about baseball's best sluggers, but he really ought to be. No one barrels up the ball quite like he does, even accounting for his too-high strikeout rate of over 27 percent. 
Now, since barrels are such a high-value type of hit, collecting them tends to lead to good outcomes. Gregory Polanco, for example, has barreled the ball 22 times and come away with 22 hits, a perfect 1.000 average that he shares with 15 other big leaguers who have had 10 barrels. Manny Machado is 35-for-45, for example, a .773 average. George Springer is 39-for-45, an .867 mark. But at the other end there's poor Paulo Orlando, Joe Mauer and Rickie Weeks Jr. -- the only three big leaguers with at least 10 barreled balls to end up with a .600 average or lower. 
You can turn it around and do the same thing for pitchers, too, because obviously if we're talking about the type of batted ball that surrenders an average of well north of .500, allowing too many of those will not end well for you.
Lowest percentage of barrels per plate appearance, 2016 pitchers, minimum 200 balls in play
1. 1.3 percent -- Rich Hill
2. 1.6 percent -- (tie) José Fernández /Blake Snell
4. 1.8 percent -- Noah Syndergaard  
5. 2.0 percent -- (tie) Gerrit Cole /Steven Wright
7. 2.2 percent -- Tyler Anderson
8. 2.3 percent -- Kyle Hendricks
9. 2.4 percent -- (tie) Joe Ross /Jake Arrieta

Gif: Gerrit Cole come backer
At the high end of that list, you'll find Chris Young (8.4 percent) and Shelby Miller (6.7 percent), which makes sense given their struggles. This tells us a lot about why Hill has been so fantastic when healthy, how Arrieta and Hendricks have helped their elite defense make them look so good and how Anderson has survived Coors Field -- they just don't allow batters to square them up.
By the way, if you lower the minimum to 150, you'll get an interesting name atop the list: Milwaukee's Blaine Boyer, who's allowed only two barrels. Why is a little-known reliever for a non-contending team so interesting? Because he's managed to survive with a slightly above-average ERA this year despite an unthinkably low 24 strikeouts in 63 innings. If you're not missing bats, you'd better be great at something. This is that something, because the list above of lowest barrel percentage contains some impressive pitchers, which indicates this may be a repeatable skill. That a pitcher like Boyer can stick in the big leagues despite other limitations shows that this may be how he's doing it.
As we continue to roll out barrels, you can follow along on our hitting and pitching leaderboards, where barrels and percentage of barrels are tracked. It's a new way to track hitters and pitchers, and use numbers to add to the scouting reports we have on these players. Preventing or collecting barrels, depending on what side of the ball you're on, looks like something that makes the best stand out.