Sinkers, Four-Seamers, and Guys Who Throw Both

If you wanted to design a puzzle to attract my interest, you couldn’t do much better than pitchers who throw both sinkers and four-seamers. I love thinking about pitching. I love thinking about fastball spin, and I’ve been having a blast looking at approach angle recently. Want to kick it into overdrive, though? Add in platoon splits, and we’re really cooking with gas.

One of those weird, of-course-this-exists-but-we-don’t-talk-about-it splits is groundball pitchers against flyball hitters and vice versa. I first learned about this split in The Book, and while it’s always made sense, Alex Chamberlain put it into a pretty picture recently that brought it back to mind for me:

fly ball hitters perform better against ground ball pitchers, and ground ball hitters perform better against fly ball pitchers

(y-axis: pitcher influence on launch angle
x-axis: hitter LA, absent pitcher influence
colors: hitter wOBAcon bins) pic.twitter.com/K43Kj868T5

— Alex "Oxlade" Chamberlain (@DolphHauldhagen) January 21, 2022

There are some terms you might not know on there, like pitcher influence on launch angle. For that, you should read Alex’s work on launch angle here. Honestly, you should probably just read all of Alex’s stuff anyway – but particularly for this, his work is invaluable.

The key takeaway here? Against groundball hitters, sinkers are an excellent choice of pitch. The hitter tends to hit the ball into the ground and sinkers generally influence launch angles downward. The result is frequently a grounder, which is great for the defense. Similarly, if you’re facing a fly ball hitter, you want them to hit it even higher into the air, which means a four-seamer with solid rise is the ticket.

The opposite is true as well. If you throw a groundball hitter a four-seamer, you’re influencing their launch angle upwards. What’s upwards of a grounder? A line drive, which is definitely not where you want to be. The same goes for sinkers to a fly ball hitter – line drives are pretty close to automatic hits (relative to other batted ball types) and produce plenty of extra bases as well. If you’re picking your fastballs, who you’re throwing to matters.

To some extent, these are just natural characteristics of baseball players. Jacob deGrom has a dominant four-seamer. If he faces off against a groundball hitter, do you know what he’s going to do? Use his four-seamer anyway, and probably embarrass the hitter with it. The small benefit that comes from the two players’ relative tendencies doesn’t erase the fact that one of them is the best pitcher in baseball.

But that doesn’t mean it’s not an interesting question to ponder, particularly for pitchers who throw both types of fastball. If you can pick which one to throw, it stands to reason that you would do some optimizing, throwing the fastball that best matches up with the hitter you’re facing. But do pitchers do that? I decided to find out.

I took every pitcher who threw at least 100 innings in 2021 and threw a sinker and a four-seamer each at least 10% of the time. That worked out to 49 pitchers of varying quality, from Zack Wheeler and Brandon Woodruff down to Joe Ross and Matt Harvey. For each of these pitchers, I also calculated a “neutral” four-seamer percentage. That’s the percentage of their fastballs (cutters excluded) that are four-seamers. Using Wheeler as an example, he threw 42.6% four-seamers and 18.2% sinkers per Pitch Info. That works out to 70% of his non-cutter fastballs being four-seamers.

Next, I took every hitter with 100 plate appearances in 2021 and sorted them by groundball rate. I labeled the 25% of batters with the lowest groundball rates “extreme fly ball hitters” and the 25% with the highest “extreme groundball hitters”. Finally, I looked up every pitch that our cohort of two-fastball pitchers threw to these two extreme groups and took their four-seamer percentages in each.

Let’s use Wheeler as an example again. He threw 529 fastballs to our high-grounder group, 71% of which were four-seamers. On the other hand, he threw 327 to our high-fly-ball group, of which 75.2% were four-seamers. In other words, his four-seamer percentage went up by 4.2 percentage points when he faced a group that does relatively worse against four-seamers. Good work, Zack!

In fact, good work everyone. If you weight each pitcher by the lesser of the pitches they threw to each group (to keep a pitcher who rarely faced one group from skewing the data), our two-fastball pitchers behaved rationally overall. They threw four-seamers 1.6% of the time more frequently to fly ball hitters than to the high-grounder group.

That’s lower than I would have expected, and some pitchers didn’t follow my generic advice (match pitches with batter types) at all. Eleven pitchers split the other way – more four-seamers to groundball hitters – by at least one percentage point:

There are some interesting names on here, but I’m most interested in the Reds duo. Castillo splits his fastballs evenly overall, and in my estimation the sinker is the better of the two. That pitch runs a 66% groundball rate, which is downright excellent, and his four-seamer is middle-of-the-road. That argues for more sinkers overall – but the way he splits the difference, throwing more sinkers to fly ball hitters than to groundball hitters, doesn’t make much sense to me. Just throw more sinkers to everyone!

Gray is a similar case. His four-seamer doesn’t miss many bats, and his sinker gets a pile of grounders (and actually misses more bats than his four-seamer, what the heck?). Yet against hitters who are predisposed to put the ball on the ground, he doesn’t force the issue with his best pitch. The fact that he and Castillo both use so few four-seamers against fly ball hitters (and vice versa) makes me think that it’s an organizational or catcher-driven philosophy, rather than something the pitchers are choosing to do on their own.

For completeness’ sake, here’s a list of all the pitchers whose four-seamer frequency increases by at least five percentage points against fly ball hitters:

These guys are doing it right, which means a) that they’re getting the most out of their stuff and b) that there’s less of a quick fix. Meanwhile, the other side of the list screams out for tinkering. Castillo and Gray are both rumored to be on the trading block, and if I acquired either of them, I’d give them a sinker pep talk. Use your best pitch more often, particularly against hitters who are bad at hitting it, and you’ll prosper. That so-so four-seamer? Save it for the batters who already swing under pitches and see if you can beat them with a taste of their own medicine.

With the main point of this article out of the way, it’s time to address some potential problems with this study. First, “four-seamers” and “sinkers” aren’t monoliths. Pitches with those classifications can look completely different, and they sometimes get mis-classified as each other.

Second, there’s a game theory aspect to this that I’ve completely ignored. The groundball hitters are poor against sinkers, so clearly you should throw the sinker. On the other hand, they know that they’re poor against sinkers and so will be looking for it, so clearly you should not throw the sinker. On the other hand, they know that you know that they’re poor against sinkers and so will be hunting sinkers, so perhaps they’ll expect you to zag and throw four-seamers. Clearly, you should throw the sinker. The correct solution is surely some mixed strategy, but I’m fairly sure it involves using your pitches against batters who struggle against them.

As a check, I looked into whether those two hitter groups actually performed worse against the pitch types that I’d expect them to struggle with. Luckily, the data backed up both the overall trend and my intuition. All batters performed better against four-seamers than sinkers in 2021 – but the extreme groundball hitters were much better against four-seamers, by more than half a run per 100 pitches. Extreme fly ball hitters were roughly equal against both types of pitches.

With the conclusion reached – trade for your favorite Red and tell them to throw sinkers to groundball hitters – and the caveats out of the way, all that’s left to say is that it’s really fun to watch for this effect in games. I’m a sucker for crafty pitchers, guys who mix up their arsenal in an attempt to out-think the batter. This is just another chance to do it, and while it’s not quite as easy as noticing a changeup to an opposite-handed batter, it’s a neat effect nonetheless.