Looking into the Heart Zone

For years now, a simple message has been gaining traction in major league bullpens and pitching labs: Just throw it down the middle. As big league pitches have gotten speedier and bendier, the people who throw them have been increasingly advised to trust their stuff, stop nibbling around the edges, and attack the heart of the zone. Adam Berry wrote about the Rays adopting this approach in 2021. In 2022, Bryan Adams superfan Justin Choi looked into the numbers and noted, “In each season since 2015, when Statcast data became public, hitters have accumulated a negative run value against down-the-middle fastballs.” Last year, Stephanie Apstein documented the phenomenon in Baltimore, while Hannah Keyser and Zach Crizer did the same on a league-wide basis, describing the Rays model thusly:

Step 1: Develop unhittable stuff
Step 2: Let it rip down the middle
Step 3: Win

Just last week, Jeff Fletcher wrote that after trying and failing to get their pitchers to attack the zone more often, the Angels started putting their pitchers in the box to face their own arsenal, courtesy of a Trajekt pitching machine. “I knew my pitches were good,” said José Soriano through an interpreter, “but when I faced myself, I find out they’re really good. So I have more trust in my stuff now.” Pitches right down the middle are called meatballs for a reason, but if you’ve ever watched peak Max Scherzer demolish the heart of the other team’s lineup by simply pumping 97-mph fastballs across the heart of the plate, none of this comes as a galloping shock.

Still, I wondered whether I could find data to back up this shift in mindset. Are pitchers really attacking the zone more often? And are better pitching staffs (or staffs with better stuff) really attacking the middle of the plate more often? After all, the Angels rank 22nd in Stuff+ and 14th in PitchingBot Stuff, not to mention near the bottom in ERA, FIP, and xFIP. If they feel this good about their stuff, I’d imagine that every team does.

First of all, I need to acknowledge that we don’t have a way to know a pitcher’s intention. We don’t know where they’re trying to put the ball; we only know where it ends up. (Earlier this month, Michael Rosen introduced The Kirby Index, which uses release angles to quantify command, but this metric has its limitations and command remains a concept ripe for further study.) In breaking this down, I’m relying on two definitions of right down the middle. The first is Game Day Zone 5, the rectangle that’s right in the middle when you break the strike zone into nine equal boxes. The second is the heart of the plate as defined by Baseball Savant’s Attack Zones, and it’s much bigger. (Incidentally, zone 5 is the same in both systems.)

So far this season, 7.5% of all pitches have been located in zone 5. That’s the highest number on record, but the overall rise has been modest. Since the beginning of the pitch-tracking era, the percentage of pitches in zone 5 has risen by roughly 0.15 percentage points, and the percentage of pitches in the heart zone has increased by just over one percentage point. Overall, the answer to our first question is a yes. On average, pitchers are hitting the heart of the zone an average of two or three times more often per game than they did at the start of the pitch-tracking era. That’s not an enormous difference, but it’s a little easier to see these trends if we break things down by pitch type. (Because the graph below is a little busy, I’ve smoothed it out by combining the data in chunks of two years rather than one, except for 2024. So the 2009 figure is actually 2008 and 2009, and 2011 is actually 2010 and 2011, and so on.)

The graph makes it clear that the increase has been driven entirely by fastballs. Four-seamers have been rising steadily, whereas sinkers have taken off just in the last few years. On the other hand, breaking balls have been hitting the heart somewhat less often and offspeed pitches have dropped fairly dramatically. The average offspeed pitch crosses the plate four inches lower this season than it did in 2008.

Next, I broke things down by team and year from 2021 through 2024 to see whether a staff’s stuff was correlated with hitting the middle of the plate more often. For example, this year, the Mets have hit the heart of the zone least often, at 24.9%, while the Brewers have hit it most often, at 27.9%. A spread of just three percentage points isn’t enormous (and the spread for pitches in zone 5 is just 1.7 percentage points), but using a sample of 30 teams over four years, there’s enough data to come away with some conclusions. Using PitchingBot and Stuff, I found that there was essentially no correlation between stuff grades and the overall percentage of down-the-middle pitches. However, there was a correlation to the percentage of down-the-middle four-seamers. Teams that have better stuff aren’t necessarily throwing more pitches down the middle overall, but they are throwing more of their fastballs down the middle. For Stuff+ the correlation is .18, and for Pitching Bot it’s .17. Those are small numbers, but the correlations get a bit larger if we look at overall performance. The correlation between the percentage of fastballs over the heart of the plate and FIP- is -.37, and the correlation to ERA- is -.35. Team with better stuff, and teams that perform better overall, really do throw more of their four-seamers right down main street.

I diced these team numbers one more way, this time comparing certain performance metrics both inside and outside the heart zone to stuff grades. (To be clear, these were the team’s overall stuff grades; there was no way for me to separate out their stuff specifically on pitches over the heart of the plate.) Obviously, most of those performance metrics are better for the pitchers outside the heart of the plate. You’ll earn more whiffs and allow fewer hard-hit balls when you’re not throwing meatballs. However, I was surprised to find that the correlation between stuff and performance is a bit weaker over the heart of the plate. For example, on pitches over the heart of the plate, Stuff+ and hard-hit rate have a correlation coefficient of -.32. Outside the heart of the plate, that correlation coefficient is -.42. Wherever you throw the ball, having better stuff will result in fewer hard-hit balls, but that stuff is less of a differentiator right over the middle of the plate. I guess I was surprised because I figured anybody can induce a weakly hit ball if they’ve got you chasing or swinging at a pitch right on the corner, but it takes better stuff to make you look bad on a pitch right down the middle. It turns out this is wrong; better stuff plays up everywhere, but even more so outside the heart of the plate. Once you’re throwing a meatball, the quality is less important. I think this illuminates the complexity of the issue, because to some extent, there’s a lie at the heart of the “Throw It Down the Middle” School of Pitching.

If you have great stuff, it’ll play up anywhere, so it’s safer for you to throw it down the middle than it is for some lesser pitcher. But obviously, hitting the corner or throwing a tempting pitch outside the zone would still result in better outcomes for you, and your stuff would play up even more out there. It’s just that hitting the corner isn’t so easy, and trying to do so comes with its own downsides. I firmly believe that throwing pitches with conviction makes a huge amount of difference. It’s one of the reasons that players like Yadier Molina and Christian Vázquez have never wanted for a job, even when the numbers didn’t love them. Pitchers trust them completely. A pitcher who believes in their stuff, who has been conditioned to challenge batters, is going to get better results. They’re not trying to be too fine; they’re letting it rip. And regardless, if they’re consistently aiming for the middle of the zone, they’re going to throw fewer balls, be ahead in the count more often, and allow fewer walks. That on its own might be worth allowing a few more hard-hit balls or losing a few whiffs.

The brings us to the last piece of the puzzle: command. While writing and researching this article, I kept coming back to something Lance Brozdowski said last July. Brozdowski was responding to a clip of Shohei Ohtani hitting the edges of the zone over and over again last summer. The thing is, on nearly every pitch, the catcher flashed a target that was in the very center of the plate. The catcher was basically caressing zone 5. “This is perhaps the best example of ‘let your miss take you to the edges of the zone’ that I’ve ever seen,” Brozdowski wrote, “particularly on his fastballs.” Brozdowski put a 40 grade on Ohtani’s command, but explained that when the catcher sets up in the middle, “he lets it eat & his stuff is bananas good.” A player like Ohtani can aim for the center of the zone, miss by a bit, and end up on the corner. Even if he misses right down the middle, his stuff is good enough to survive some meatballs. Furthermore, even if he doesn’t miss at all, he’s got a good chance of ending up on a corner anyway. Sticking with Ohtani as an example, I’ve taken his 2023 movement profile from Brooks Baseball, then overlaid it on a Baseball Savant diagram of the strike zone at the proper scale. (Ignore the big dots on the left and right; in order to get a clean diagram of the zone, I searched for all the times Ohtani hit a batter with a pitch. This is why batters wear elbow guards.)

If Ohtani had perfect command and simply threw each pitch so that it started out headed directly for the center of the zone, everything except for his cutter and his four-seamer would end up right on the edge of the zone. (Also, a four-seamer located up in the zone like that, especially Ohtani’s four-seamer, is definitely not a bad pitch) And again, that’s just if he aims for and hits his intended target in the center of the strike zone before it breaks. Now not every pitcher has stuff as good as Ohtani’s, but the lesson remains the same. Aiming down the middle and missing on the corner is a strategy that makes a lot of sense.

Whether it’s because throwing pitches down the middle is a good thing, or it’s because trying to do so comes with all these ancillary benefits, the plan does seem to be working. As long as stuff keeps improving, just chucking it right down the middle will make more and more sense for pitchers. That’s obviously not the case for everyone. If Kyle Hendricks aims right down the middle, he’s going to throw it right down the middle, and that’s not going to work out so hot. If this were 30 years ago, when more pitchers lived by command and there was a bigger strike zone that offered more safe places to put a pitch, the numbers I’ve shown you might look very different. But in today’s game, when there’s a surfeit of pitchers who have the stuff but might lack either the command or the conviction, getting right to the heart of the matter is here to stay.