Does Throwing a Pitch More Alter Its Effectiveness?

Pitchers are relying on their best pitches more and more. And why should they not? It makes all the sense in the world. Throwing a fastball 60% of the time just so that you can “establish it” is an outdated moniker that players and teams alike are reticent to follow. Take a look at the our season stat grid tool if you want proof that the most dominant pitchers in the league are increasingly relying on their breaking pitches. Select curveballs and you will see Julio Urías, Zack Greinke, Brandon Woodruff, Anthony DeSclafani, Dylan Bundy, Walker Buehler, Corbin Burnes, and John Means toward the top of the list. For sliders, that list features Tyler Glasnow, Lance McCullers Jr. (who is also throwing a new slider), Shane Bieber, a new and improved Jeff Hoffman, Freddy Peralta, and even Clayton Kershaw, whose slider is almost 45% of his pitch diet.

These are cherrypicked examples; not every pitcher on this leaderboard has been as productive as those starters thus far. But it does point to the idea that the best pitchers MLB has to offer are increasingly leaning into their best secondary offerings and have either continued to be successful or found another level in their production.

The idea of simply throwing your best pitch has become more in vogue in recent years. Back in 2017, Eno Sarris wrote that pitchers should try making breaking balls 80% of their total pitch mix. Part of the reason is that non-fastball pitches, specifically breaking balls, have gotten increasingly harder to hit; Ben Clemens wrote about this trend a couple of years ago. Even though fastballs have become harder to hit by virtue of increased velocity, pitchers are turning away from them in favor of other offerings.

This decision raises the question: Are pitchers successful with their non-fastball pitches because they use them less? The idea is that the main driver of offspeed or breaking ball success would be that hitters see them less, making them tougher to adjust to in a plate appearance. Theoretically, then, if a pitcher goes primarily to his secondary pitches, those pitches will become less effective on a per pitch basis. Is this true?

To investigate, I took every pitch type that was thrown at least 100 times in a season from 2018 through ’20. I took the year-over-year changes in pitch usage, swinging-strike rate, and run value per 100 pitches thrown for each season pair (where in both seasons the pitch was thrown on 100-plus occasions).

The first thing I wanted to look at was effectiveness based on changes in usage for each individual pitch type. The short answer to this is that there is little relationship between marginal usage change and marginal success in either of the two measures for any pitch type.

If anything, changeups and curveballs actually induce swinging strikes as a higher percentage of all pitches with more usage. That is the strongest relationship in this dataset, and it still consists mostly of noise. Based on the data, there is no evidence that pitchers should be dissuaded from throwing their best pitches more often, and that holds true for breaking balls, offspeed pitches, and fastballs.

Sure, you may argue, throwing any pitch a little more won’t have adverse effects on its effectiveness, but aren’t there diminishing returns? At a certain point, don’t you throw the pitch too often to fool the batter? To answer that, I placed each pitcher and pitch type pair into a bucket based on usage, then separated the bucket into increments of 10% (so the first consisted of pitches thrown between 0 and 10% of the time, the second 10% and 20%, etc.). I then grouped the pitch usages across the three seasons and looked for any potential deviations in effectiveness.

Again, these relationships are mostly noise. Even for pitches thrown upwards of 70% to 80% of the time (beyond which the the data is scarce), they should not lose any per-pitch potency by virtue of increased predictability.

For those of you skeptical that fastballs make up the majority of pitches and that this lack of a relationship may not be evident with breaking balls or offspeed pitches specifically, I have bad news for you:

As with run values, there’s no strong relationship between swinging-strike rate and usage.

As noted above, fastball usage is on the decline throughout the league. But using the data I collected from ’18 through ’20, it’s clear that pitchers aren’t all now throwing breaking pitches all the time.

The vertical lines represent the 50th percentile in that specific distribution. On average, pitchers using a certain breaking ball less than 30% of the time shied away from using the pitch more. On the other hand, breaking ball usage mostly increased for players who used it more than a cursory amount. That all makes sense: If you have a breaking ball you like to use (or are comfortable using), you’re going to throw it more; if you don’t have a strong breaking pitch, then you’re not going to be tossing it all the time even if it could theoretically be more effective.

Throwing a pitch just for the sake of throwing it is not going to fly in MLB in 2021. Pitches are thrown with a purpose: generating whiffs, or at least groundballs. This is one of the fundamental factors in the ever-increasing strikeout rate: Not only are pitchers throwing harder than ever, but they are also leaning on their best stuff even more. That’s while every one of those pitches is being optimized with the help of technology to generate maximum movement and deception. And that trend will not stop until there is evidence that a pitch will perform worse upon increased usage. Barring that, pitchers across the league will rely on the pitches they deem most dominant.