Among the many reasons Major League hitters are having a tougher time putting runs on the board these days is that pitchers simply aren't giving them much to work with. According to pitch tracking data, the percentage of pitches in the strike zone has fallen consistently each year from 2010's 50.4 percent to 2015's 47.8 percent, and that's a big deal, because we've learned that making contact on pitches in the zone as compared to outside it is among the most important things a hitter can do.
So if a hitter actually does get a fat pitch -- or a mistake, or a meatball, or one served on a platter, or whatever you want to call it -- he'd better be ready to do something with it, because he's not likely to get such a lucky opportunity again. But before we run down the best in baseball at taking advantage of the chances offered, an important question arises: What is a mistake, from a pitcher's point of view? We can't always know what a pitcher's intent is, and there's not necessarily one characteristic that always applies to identify those pitches.
That's both frustrating and freeing, because it allows us to define the "mistake" however we like. For these purposes, we'll keep it simple. One might think that it's as basic as pitches right down the pike, but there's ample evidence that balls low in the strike zone are a hitter's friend, too, as shown by the fact that the 93.1 mph Statcast™ exit velocity on middle-low pitches was actually higher than the velocity on those thrown dead center.
So we looked for pitches that fit three criteria:

1. They arrived in the middle-middle or middle-low areas of the strike zone.
   
2. They weren't faster than 95 mph, because it's hard to say that hitting 99 mph at the bottom of the zone is a problem for a pitcher.
   
3. They were not a knuckleball, because we're trying to stick with pitches from this galaxy.
   We put all that in the blender and set 40 plate appearances as a minimum baseline. It's not a perfect methodology, but whenever you're trying to find a definition for something generally referred to as a "meatball," well, you'll get differences of opinion. What we're left with are baseball's best mistake hitters of 2015. As you'll see, we're quickly crowning a king.
   Batting average on "mistake pitches" in 2015
   1. Miguel Sano, .500
   
4.  Eric Hosmer, .490
   
5.  David Peralta, .486
   
6.  Joey Butler, .480
   
7.  Ryan Zimmerman, .476
   Batting average is a flawed stat that ought to be avoided in most advanced analysis, but since we're not really interested in walks for this exercise, it'll do to start with. Sano had 44 plate appearances where he saw a meatball pitch as we've defined it, and 22 times that turned into a hit, including seven of his 18 homers. We profiled Sano here in September as "living in the line drive zone," so this makes sense -- despite the fact that no hitter in baseball saw fewer fastballs.
   Gif: Miguel Sano hits homer
   Slugging percentage on "mistake pitches" in 2015
   1. Sano, 1.159
   
8.  J.D. Martinez, 1.047
   
9.  Mike Trout, 1.029
   
10.  Nolan Arenado, 1.025
    
11. Zimmerman, 1.000
    Now we're getting somewhere. When we turn to slugging percentage, we get more Sano, along with some of baseball's best sluggers. (It was easy to miss that Martinez had 38 homers last year, but he did.) Trout's great in all situations, of course, but he also nearly doubled his .590 season slugging line by by fattening up on "mistakes." You should probably never throw Trout a hittable pitch. You should especially never throw him one of these.
    Gif: Mike Trout homer
    Exit velocity on "mistake pitches" in 2015
    1. Giancarlo Stanton, 103.0 mph
    
12.  Yasmani Grandal, 100.4 mph
    
13. Trout, 100.4 mph
    
14.  Miguel Cabrera, 100.2 mph
    
15.  Paul Goldschmidt, 99.0 mph
    Of course Stanton shows up on an exit velocity leaderboard. Of course he does, because despite missing half the season to injury, Stanton still finds his way to the top of every leaderboard we do. These are four of baseball's most elite stars, which makes sense given what we learned about how exit velocity corresponds to production, and while Grandal looks like an outlier here, remember that he was baseball's best hitting catcher before an August shoulder injury. (Sano comes in at 97.9 mph.)
    Gif: Stanton bomb
    The takeaway here? Well, pitchers should know better than to give elite hitters fat pitches, and for the most part, they do. The leaders in biggest percentage of mistakes seen, by our definition, are Sean Rodriguez (13.2 percent), Will Middlebrooks (12.6 percent), Danny Santana (12.4 percent) and Eugenio Suarez (12.2 percent), none among the more feared hitters in the game. For their part, nearly every hitter swings at these pitches between 60 and 90 percent of the time, with only Dodgers Alex Guerrero and Yasiel Puig above that mark, and Jonny Gomes and J.J. Hardy below.
    But even quality Major League pitchers can't be perfect. Sometimes, they're going to let loose a pitch they wish they hadn't, a mistake right into the danger zone against a good hitter. The best hitters don't let that pitch go by. They crush it. They have to.