It looks something like this:
The general message being sent: Mike Trout has been absolutely killing pitches down in and beyond the zone. Yet, he's been struggling against pitches up. You can see it in color form, as above, or you can see it in numerical form. Against pitches in the lower third of the strike zone this year, Trout's slugged a spectacular .875. Against pitches in the upper third of the strike zone this year, Trout's slugged a feeble .211. The former is among the best in the league. The latter's among the very worst.
Everyone's picked up on it by now. Trout, I'm sure, knows what's going on. This is information that's been noted repeatedly on ESPN and the MLB Network. Based on this, it seems like Trout shouldn't actually be all that difficult to put away. But, yeah. He's probably on course to win the American League's Most Valuable Player award. And despite what the numbers say, Trout's seen more low pitches than high pitches. To this point, 11 percent of his pitches have been in that upper third. And 14 percent have been in the bottom third. It seems odd, but Trout is just an extreme example of a league-wide trend.
We only have really good information going back to 2008, thanks to PITCHf/x. It's tough to examine league-wide trends when you're limited to less than a decade of data. But, let's do what we can. Let's compare, on a year-to-year basis, that upper third of the strike zone against the lower third of the strike zone. This chart contains six lines and a lot of information, but I promise I'll explain it all in the words that follow.
Right away, let's acknowledge: there's nothing dramatic. But, we wouldn't expect there to be; leagues don't change that fast. So we can talk about the subtle shifts. Anything apparent at this level is interesting.
Start at the bottom. Over time, the rate of pitches in the upper third has held firm. Yet, there's been an increase in the rate of pitches in the bottom third. In 2008, the difference between the rates was 1.7 percentage points. So far this year, it's 4.3. Pitchers, by and large, are working lower. The called strike zone has followed them. There's increasing emphasis on working around the lower edge.
Now look up to the next pair of lines. Hitters are swinging at the same rate of pitches in the upper third. But they're swinging at more pitches in the lower third, by a few percentage points. So, where the gap a few years ago was almost eight percentage points, now it's dipped below five. This is some kind of hint that hitters have responded to the pitchers' increased low-zone emphasis.
And now look at the highest pair of lines. These measure league-wide contact rates, and you can see the lines intersect. At the start of the PITCHf/x era, hitters made contact more often with pitches up than with pitches down. Now the opposite is true. Contact rates on pitches up have declined. Contact rates on pitches down have very slightly improved. This is another hint that hitters are looking low, leaving them a little more vulnerable up.
And here's what this has led to: in 2008, hitters slugged 30 points better against high strikes than they did against low strikes. The next season, they slugged 51 points better. Fast-forward now to 2014, and you'll observe that now hitters are slugging 10 points worse against those same high strikes. For the first time in what's admittedly a short era, hitters are slugging worse against high pitches than they are against low pitches. Not every hitter in baseball is as extreme a case as Mike Trout, but, generally speaking, hitters have focused more on the bottom of the zone, and they've made sacrifices toward the top.
Yet, pitchers continue to work down. It's how they've long been instructed, and it's where offspeed pitches are usually supposed to go. It's where the best pitch-framers are able to do their best framing. From a young age, pitchers have it drilled into their heads that they want to work down and generate weak contact. Pitches left up are pitches most likely to get knocked off of or beyond the fence.
So targets get set low, and the pitches follow. Hitters have tried to respond, and they've had some modest success. You can believe me, or you can believe a real-life MLB front office. See, this isn't my discovery. This is me taking the long way to point at someone else's work. From a recent Business Week Astros profile:
"Everybody says, 'Keep the ball down, keep the ball down,'" says [Brent] Strom. Major league teams have long favored ground-ball pitchers, since grounders tend not to result in doubles, triples, or home runs.
But here again, advanced data yielded a useful insight: Major league hitters had become so adept at hitting low pitches that they were vulnerable to high ones. Beane had discovered a particularly clever countermove. "Beane stayed ahead of the curve," says Strom, "by finding hitters with a steep upward swing path to counter the sinking action of pitchers trying to induce ground balls."
Billy Beane put together a baseball team constructed to fight those low pitches. That was part of the response. Because of the response, the upper parts of the zone have opened up again, because only the best hitters in the league are really capable of controlling all sides. The Astros had Collin McHugh start to throw more elevated four-seam fastballs, on the idea that he could zig where other pitchers continue to zag. McHugh is having an outstanding season out of nowhere, with more strikeouts than innings, and 18 percent of his two-strike fastballs have generated strikeouts.
So this is how we proceed in the league's hunt for equilibrium. For years, pitchers worked to throw down more and more often. There was a greater emphasis placed on generating grounders and avoiding balls in the air. The league has started to respond, with hitters focusing more on making good contact with those low pitches. And also with teams focusing more on finding hitters with the right swing paths. Now, for the first time we know of, hitters are slugging better against low pitches than high pitches. So now the league will eventually respond to the response, re-establishing the upper parts of the zone. McHugh is one example, but it seems it'll be a while yet before more pitchers resume elevating. For now, they're still doing what they've always been told, and they're pitching to their own strengths instead of to the hitters' weaknesses. That's basically how we get a 2014 Mike Trout. The response to Trout seems obvious, but it's hard to go against one's own track record. And then, in time, there would just be a response to the response to the response. Look closely enough and there's no such thing as equilibrium at all.