How Variety and Repetition Impact Pitching and Hitting Performance
How does arsenal size and usage impact pitcher and hitter performance?
At Oyster Analytics, we normally stay away from pitch evaluation, since there are about ten thousand stuff+ models out there and nearly the same number of people working on visualizing and analyzing Savant data in almost every combination. That’s fantastic to see, but it also makes it an area we’re less inclined to pile into.
With that said, today, we’re taking a trip along one of the less-traversed roads in the vast network of pitch analysis. We’re not making any claims about the value of individual pitches, but are instead here aiming to demonstrate how variety and repetition in pitch sequencing shapes hitter performance and pitcher longevity (both in games and in counts).
By now, we all know that pitchers tend to get worse the more they see hitters, with starters often getting pulled before their dreaded third trip through the order. But can the severity of that decline be altered by pitch selection? Is there a difference between facing a batter for the third time if you’ve got six pitches to throw at him vs. if you’ve already shown him each of your three offerings multiple times? Do batters get better within counts after seeing what a pitcher has to offer and getting their eyes on the same pitch multiple times?
In a word, yes. Generally, the more times a batter sees a pitch, the better they do against it–even controlling for time through the order. Conversely, the more times a pitcher throws the same stuff in a game and within a plate appearance, the worse they tend to perform. You could stop reading now, but this broad overview obscures a lot of meaningful nuance. Here, we highlight six key findings from our analysis.
Note: This analysis uses Statcast data from 2021-2024, starting pitchers only
Multiple Shapes of Breaking Stuff Increases Overall Longevity
A Few Changeups a Day Keeps the Bullpen Away
Larger Arsenals = Slower Drop Off
Emphasizing Variety in Pitch Calling Gets the Most Out of Pitchers
Throwing Gas is Great, But Its Advantage Fades Within Plate Appearances
Novelty Matters Most for Changeups and Breaking Balls
1. Multiple Shapes of Breaking Stuff Increases Overall Longevity
Generally, pitchers who can show batters multiple shapes of breaking stuff fare better as the game goes on. To us, this tracks logically: if a batter can know exactly what movement he should expect as soon as he identifies spin, he’s probably more able to adjust to that pitch than if there are multiple potential movement profiles he could face. What’s more, as we’ll discuss later, hitters generally fare better against breaking balls the more they see them–having two different breaking balls enables pitchers to show less of each one to each batter throughout the game.
The data is pretty clear here: pitchers who throw at least two shapes of breaking stuff better maintain their overall whiff rate as they go through the order multiple times. To qualify as throwing two breaking balls here, a pitcher needs to throw each offering at least 10% of the time.
Change in Whiff Rate From First Time Through the Order, by Number of Breaking Ball Shapes
Within at-bats, a similar phenomenon emerges. As pitchers with a lone breaking ball throw their hook more, its effectiveness decreases faster than breaking stuff dealt by pitchers with a pair of spinners. The effect is most pronounced for sliders, as shown in the figure below.
Change in Whiff% Relative to First Time Seeing Pitch in PA, by Number of Breaking Ball Shapes
As pitchers get deeper into counts, hitters adjust to breaking stuff more quickly if it is the only spin pitchers feature. For example, against pitchers with multiple breaking balls, if a hitter has seen three sliders in a count, they’re whiffing 16.8% less often than they do on the first slider they see. By contrast, they’re only whiffing 11.5% less often on that third slider if a pitcher features another spinner at least 10% of the time.
Why you should care: Aside from, “Huh, that’s interesting” (hopefully), the takeaway here is that assortment in breaking stuff can propel pitchers deeper into games more successfully, and enable them to win long battles with hitters. Starters who have typically been five and fly guys who added new variants to their spinners going into the year are candidates for increased longevity in 2025.
New Spin Guys to Watch For: Jackson Jobe, Casey Mize, Max Meyer, Graham Ashcraft, Kyle Harrison (sourced from a great article outlining who’s been working on new pitches this ST)
Two-Shape Workhorses: Gerrit Cole, Paul Skenes, Logan Gilbert,
One-Shape Mold-Breaking Workhorses: Tarik Skubal, Logan Webb, Aaron Nola
2. A Few Changeups a Day Keeps the Bullpen Away
Throwing a changeup also, on average, enables pitchers to stifle hitters deeper into games and counts. As pitchers get deeper into games, whiff rate degenerates faster for those starters who do not feature a changeup (10%+ usage) than it does for those who do.
Whiff Rate Change from First 30 Pitches, Pitchers Who Feature a Changeup vs. Pitchers Who Do Not
Those differences aren’t massive, but we’re looking at a dataset of over 1.5 million pitches here–the margins don’t have to be huge to indicate a real difference.
The emphasis in the title of this section, though, is on “a few” changeups. The first changeup a hitter sees in any given plate appearance is much more effective than those subsequent, as shown in the figure below.
Whiff Rate on Changeups by Changeups Seen This Plate Appearance
Batters whiff on 32.1% of the first changeups they see in their first plate appearance, but if they’re lucky enough to see it three times, they whiff just 23.8% of the time on that double encore rendition.
The takeaway here for pitchers is that featuring a changeup frequently enough that it is present in the hitter’s mind and can’t be ruled out as a legitimate pitch is beneficial for deep innings success. Even then, they should avoid showing the same batter the same changeup too often. But more importantly…
Why you should care: Monitoring changeup usage can give us an inside track on what guys might go deeper in games this year. It’s tougher to predict how good these guys will be–with changeups, it’s less about adding the pitch (almost everyone throws a changeup at least once in a blue moon) and more about finding out who’s ready to use it as a bonafide offering.
3. Larger Arsenals = Slower Drop Off
So, we’ve told you that throwing multiple breaking balls is good for longevity and the ability to win prolonged battles at the plate. We’ve also told you that featuring a changeup at least 10% of the time boosts one’s ability to stay effective longer in games and within at-bats. Put those together, and it would seem as though we’re suggesting that larger arsenals typically lead to deeper success.
Thankfully for the structure of this article, this third puzzle piece clicks into place. Pitchers who mix more (amount of unique pitches thrown 10%+ of the time) typically see their performance fade less quickly as they get deeper into games.
Change in Whiff% Relative to First PA, by Arsenal Size
Throwing five pitches or more is a major boost for pitchers as they get deeper into games. Pitchers with five or more pitches deteriorate less by the third time through the order than pitchers with just three pitches do by the second time!
Why you should care: As a Down on the Farmer, you now have the inside scoop on which pitchers are new-age five and fly guys that commentators will rage against, and which are workhorses who exemplify everything great about the good old days. These findings bode well for guys like Will Warren, who’s flexed five pitches in spring training, including an improved changeup, and Kodai Senga, who appears to have added a splinker to his offerings.
4. Emphasizing Variety in Pitch Calling Gets the Most Out of Pitchers
Pitchers can get the most out of their arsenals, whatever the size, by endeavoring to exhibit a large degree of variety in the pitches they throw in any one plate appearance. We’ve calculated a “variety score” that is, for each plate appearance: the number of distinct pitches thrown by the pitcher in that plate appearance divided by the total number of pitches in that plate appearance, scaled as a percentile of all of of that pitcher’s plate appearances in which they threw at least three pitches. This enables a comparison of variation that does not get complicated by the different effectiveness/deterioration through counts of different pitchers—each pitcher is only being compared to himself.
On average, the higher a variety score a plate appearance has, the worse a hitter does in it. This effect is visible in three and four pitch plate appearances as well, but really becomes clear once plate appearances hit five pitches or more, as shown in the figure below.
wOBA in 5 or More Pitch PAs, by Pitcher-Specific Variety Score
We Down on the Oyster Farmhands are always anticipating potential objections, and there’s a clear one here. Couldn’t this just be due to the fact that more variety typically means more soft stuff, which gets better results? If a variety score is low, it’s more likely to be due to a proliferation of fastballs rather than other stuff, so maybe all this is just a measure of off speed usage. Or, is it possible also that there’s a correlation between variety score and plate appearance length, and that it’s simply that longer at bats have both better hitter performances and lower variety scores?
Neither of these two potential confounders explains the relationship between variety score and performance. The chart below filters down to just five pitch plate appearances featuring two fastballs, and illustrates a magnified version of the first chart (don’t worry, even with these very specific filters there are still over 18,000 PAs to work with).
wOBA in Five Pitch PAs Featuring Two Fastballs, by Pitcher-Specific Variety Score
However you slice it, the message is clear: variety is good.
Why you should care: Just because your favorite pitcher hasn’t added a new pitch in Spring Training doesn’t mean they can’t improve their performance in deep counts. Pitch calling is a complex art, and we make no claims to have all the answers, but it does appear pitchers can get more out of whatever arsenal they are working it by making mixing it up a priority.
5. Throwing Gas is Great, But Its Advantage Fades Within Plate Appearances
Throwing gas is always good, but it becomes less useful as hitters see more of it in the same plate appearance. Hitters always whiff more on high-velocity fastballs than low-velocity ones, but the gap shrinks substantially the more fastballs a batter sees. The chart below shows what we’ve termed ΔWhiff, which is the difference in whiff rate relative to the average whiff rate on that time through the order and pitch number within the at-bat. What this chart below shows, then, is controlling for time through the order and overall pitches seen in that plate appearance by the hitter, high-velocity fastballs lose some of their advantage over low-velocity fastballs the more times a hitter sees fastballs.
ΔWhiff by Fastballs Seen in Plate Appearance
Why you should care: This reveals that while high-velocity fastballs are still overall more effective than slower heaters, hard-throwers regress more mid-plate appearance.
6. Novelty Matters Most for Changeups and Breaking Balls
It’s clear that hitters are able to adjust to higher velocity fastballs within plate appearances in a way that negates some of these pitchers’ gas-fueled advantage. But how good are hitters at adjusting to other types of pitches within a plate appearance?
It turns out, they’re actually the worst at adjusting to fastballs. It’s the slow stuff that hitters get better at hitting the more they see it. Hitters whiff 19.0% less often on changeups the third time they see them than they do the first time they see them, within the same plate appearance. On fastballs, depending on the type (four-seam, sinker, cutter) that decline is between 7-11%. Breaking stuff falls somewhere in the middle, with hitters whiffing 12.5% less on the third curveball they see than the first, and 14.6% less on the third slider they see than the first.
Change in Whiff% Relative to First Time Seeing Pitch in PA
There is an interesting exception to this general rule: on 0-2, pitchers actually benefit from repeating pitches, especially if they have the opportunity to throw a pitch for a third consecutive time. Our only explanation of this is that it’s a bold way to win a mind game with the hitter— “surely he won’t throw it a third time…” is going through players’ heads ahead of an 0-2 pitch in these situations. The exception to the exception is four-seam fastballs, which we still don’t advise throwing three times in a row, but every other pitch bucks the usual trend and has a higher whiff rate the more it’s been seen on an 0-2 pitch.
0-2 Counts Only: Change in Whiff% Relative to First Time Seeing Pitch in PA
Now, it’s possible here that the reason for this is that pitchers inclined to throw the same pitch for the third time in a row are likely to have a very good version of that pitch. That may be true, but it doesn’t explain this pattern. Even if you include only the middle third of fastball types in terms of velocity, and only the middle third of breaking balls and changeups in terms of movement, the trend remains intact for all non-fastballs (cutters see reduced performance, sinkers still improve but at a lower rate than in the unfiltered data)
0-2 Counts Only: Change in Whiff% Relative to First Time Seeing Pitch in PA, Middle Third of Velocity (for fastballs) and Movement (for others) Only
Why you should care: This has meaningful implications for pitch calling. Prioritizing pitches that hitters have not yet seen, and especially not yet seen multiple times in this plate appearance, is an important aspect of pitch-calling (though of course should not be taken as an exclusive imperative). This also circles back to the positive effect of throwing 4+ and 5+ pitches, as it allows pitchers to show hitters something new in more situations than more pitch-starved peers.
Tying it All Together
The key takeaway here is simple: the more hitters see anything, the better they are at dealing with it. For pitchers, this means it is important to have a large arsenal featuring a changeup and multiple shapes of breaking stuff. It’s also important to use that arsenal in a way that minimizes the amount of times hitters see the same pitch, and particularly the same slow stuff, in the same plate appearance (without becoming robotic or predictable of course).