Last week, we highlighted how important it was for hitters to make good decisions on swinging at pitches inside the zone, and focused specifically on baseball's best "mistake hitters," or those who took the most advantage when pitchers served them up fat pitches. (Spoiler alert: Miguel Sano is awesome, always.)
Still, hitters are only human, and they're not always able to follow that good advice. After all, the legendary Yogi Berra once said: "If I can hit it, it's a good pitch." And it's basically a federal law that if Yogi said it, it's true. Furthermore, could any of us -- aside from Trevor Bauer, anyway -- pretend we weren't entertained when Evan Gattis took a pitch nearly four-and-a-half feet off the ground and crushed it into the seats last year?
Gif: Gattis crushes homer off Bauer
Of course not. So while it's not generally recommended, we can at least take a minute to recognize baseball's best bad-ball hitters. You're probably now thinking of Vladimir Guerrero, who singled on a pitch that bounced at least one time that we know of, or the famously free-swinging Pablo Sandoval, who led baseball in outside-the-zone swinging percentage in 2015 and is second only to Guerrero dating back to 2008. You know what this kind of hitter looks like.
That said, before we can come up with a list, we have to define a "bad ball," much like we did with "mistake pitches." There's the simple way, which is pitches that fall outside the PITCHf/x strike zone, which allows us to point out that balls hit within the zone average an extra 239 points of slugging percentage and 7.8 mph of Statcast™ exit velocity. There have also been far more complicated methods, like those that use advanced signal detection theory or painstakingly map out each small section of the zone for likely strikes for each hitter.
The first is too simple; after all, we're not going to penalize hitters for offering at the pitch that's just off the plate, which is technically a ball but sometimes called a strike. The second is more scientifically valid, but is a bit too much firepower for our rather straightforward purposes. So our methodology will work like this, as we're looking for:
1. Pitches that were at least 1 foot outside the PITCHf/x zone. (For high pitches, we used 3.5 feet off the ground; for low, it was lower than 1.25 feet above the ground. Arbitrary? Sure! But a "bad ball" can be anything you want it to be.)
2. Minimum 20 plate appearances with a "bad-ball" swing for individual leaders
3. Swinging strikes included, because that's the most likely outcome of these bad pitches
Now: Unlike "mistakes," which were all in the same spot for everyone, we're talking about different skills. The hitter who steps across the plate to make contact in the opposite batter's box probably isn't the same hitter who leaps out of his shoes to get one at his eyes or who drops to one knee for a pitch in the dirt. So let's recognize that, and break these down into four categories: High, Low, Outside (righty hitter), and Outside lefty hitter). Onward!
High pitches
MLB
Slugging: .223
Batting avg.: .140
Individual
Slugging: Jay Bruce, .696; Justin Bour, .647
Batting avg.: Brian McCann, .348; Prince Fielder, .333
High pitches are fascinating, despite ample evidence that pitchers from Chris Young to Drew Smyly to Justin Verlander to Adam Ottavino are finding success with high fastballs. The truth is that a poorly-placed or spun pitch up in the zone, or above it, can still be hit a long way. McCann, for instance, hit a pitch that was four feet and three inches off the ground -- off of the aforementioned Young, no less -- for the highest home run hit by a lefty all season.

Bryce Harper was third in slugging on these pitches. There's probably not a leaderboard you could come up with that wouldn't have Harper, the unanimous National League MVP Award winner, high on it. Remember, we're talking about the guys who are best at hitting the worst pitches. He's even good at that!
Low pitches
MLB
Slugging: .166
Batting avg.: .133
Individual
Slugging: Dee Gordon, .429; Jose Reyes /Jason Kipnis, .414
Batting avg.: Gordon, .367; A.J. Pierzynski, .333
You'll notice that Gordon and Reyes are both known for their speed, but not a single ball here was a bunt attempt -- though several were infield singles, and one was even marked as a "single to catcher Travis d'Arnaud." A few of the well-placed ones right down the line turned into doubles and triples, which is why he leads in slugging percentage too.
On that note, let's call special attention to where Gordon's bat had to get to manage this triple off Chris Heston on July 1, when Buster Posey's glove is actually touching the ground:

At contact, the ball was 5.4 inches off the ground. It cost Heston three bases and a run -- more than a run, really, because Gordon would end up scoring on a double play. Poor Heston. No one is supposed to hit that, because no one is supposed to swing at that.
Outside (righty hitter)
MLB
Slugging: .190
Batting avg.: .170
Individual
Slugging: Gattis, .417; Justin Turner, .409
Batting avg.: Josh Harrison, .351; Alex Rios, .320
Harrison dumped his share of well-placed soft liners into right field, but he also benefited from a double on a play marked with the memorable description of "Josh Harrison doubles (9) on a popup to left fielder Chris Coghlan, deflected by shortstop Starlin Castro." That's actually a recurring theme; he had two other hits on deflections.
Are you at all surprised that Gattis showed up here? Of course not. Is the fact we already used a Gattis GIF earlier going to stop us from using another? Also, of course not.
Gif: Evan Gattis Home Run
Outside (lefty hitter)
MLB
Slugging: .260
Batting avg.: .216
Individual
Slugging: Mark Teixeira, .667; Tyler Collins, .636
Batting avg.: Teixeira/Collins, .500
You're maybe noticing that the numbers for lefties here are better than righties have, and that's not an accident. It's a little-known fact that lefty hitters and righty hitters actually face different strike zones, with one study indicating a difference of 23 square inches in 2015. (Short version: The zone tends to skew a little farther outside for lefties than it does for righties.) A more rigorous study would have adjusted for that here, but for the purposes of this exercise, it's more important just to know the difference exists.
As for the leaders: Collins actually managed three doubles on "bad balls," impressive given that he had only 11 all season. Teixeira? Well, he's built a career on these kinds of things. No, really: Since joining the Yankees in 2009, he's got 53 hits on pitches just like this.