What is Being Thrown: Pitch Usage in 2021

Several weeks ago I took a rough hack at quantifying the variation of any given pitcher’s pitch mix. As a step back, and tangential extension of that exercise, below is a very general summary of what types of pitches are being thrown this year. Simply put, what follows should address: what pitches are being thrown the most, what are the most common pitch mixes (by pitch types), and how many distinct pitches pitchers are throwing to this point in 2021.

It is still relatively early in 2021, so only pitchers who have thrown at least 500 pitches (at the time data was pulled) are included so as to only include those whose repertoires are a bit more established. In today’s low pitch count environment, that corresponds to maybe 6 starts and establishes starting pitchers as the primary players in this outline. Altogether, 133 pitchers were included; all data comes via Baseball Savant. While pitch classification is an imperfect science, Baseball Savant seems to do a really good job distinguishing between pitcher offerings.

To start, a quick breakdown of the number of pitches of each classification thrown by this group.

It’s first worth noting that the 8 pitches classified only as “fastballs” by Baseball Savant were all attributed to Zack Greinke. Additionally, the 2 pitches classified as “Eephus” were attributed to… Zack Greinke.

Slider usage has eclipsed that of both sinkers and changeups in a game that presently values spin so highly. Curveballs have been split into both traditional and knuckle curve varieties, the latter of which is used by high profile starters like Trevor Bauer, Gerrit Cole, Shane Bieber, and Aaron Nola. Even taken together though, the slider is the breaking ball of preference among today’s starters, it appears.

Among 9 pitch classifications (I exclude Zack Greinke’s ambiguous “fastball,” for better or worse), there are an incredible number of possible permutations for any given pitcher’s pitch mix. However, below are the most common. Pitch classes have been hyphen-separated with blank spaces between hyphens in the case of the exclusion of any given pitch from that mix.

Despite the considerable number of possible pitch usage permutations, there were in fact 37 distinct sets of pitch mixes among the 133 players in the group. Of those 133 pitchers, just over 20% relied on the five pitches in the first row. There was less overlap than I, for one, anticipated; the vast majority of pitch mixes (24 of 37) were used by either just 1 or 2 individual pitchers.

Next wishing to see how these outcomes changed by excluding uncommon pitch usage, I (completely arbitrarily) removed pitches thrown <5% of the time. Below are the results.

Interestingly, the exclusion of pitches thrown less than 5% of the time did not consolidate the number of pitchers utilizing the same pitches but rather left them even more dispersed. After the exclusion, there were 48 distinct pitch mixes across those 133 pitchers.

To address the final question originally posed above, below are two charts which very simply group pitchers by the number of distinct pitches they throw. The first chart includes all pitch types (save for Zack Greinke’s “fastball”, yet again) while the second includes pitches thrown at least 5% of the time by any given pitcher.

More than half of the 133 qualifying pitchers throw 5 or more pitches, according to Baseball Savant. Perhaps unsurprisingly, the sole pitcher with 8 distinct pitches is Yu Darvish. No single pitcher included threw just 2 distinct pitches. Predictably though, those numbers dip once infrequent pitches have been excluded.

Given the pitch percentage threshold imposed, a single player (Brady Singer) throws just two pitches. Otherwise, the number of pitches thrown by pitchers appears to be essentially normally distributed around 4. Of course, 5% was essentially chosen at random as a threshold here, and there is value in a pitch a starter might defer to as many as 5 times in a 100 pitch start.

To recap, these pitchers are throwing a lot of different types (more often than not, 5 or more) of pitches in 2021, the majority of which feature high spin rates. Despite that preference, the variety of pitch mix permutations is still quite rich, with just ~20% of pitchers throwing the most common set.