“Stuff” and Father Time

The question of how pitchers age is paramount to players and front offices. “Stuff,” the colloquial term for raw talent throwing the baseball, can really be boiled down to velocity and movement (if we really wanted to oversimplify things). PITCHf/x gives us an opportunity to use big data to estimate “stuff” by looking at measurements of velocity and movement. We can use the copious data collected to estimate what “stuff” we can expect from pitchers as they pass the dreaded 30-years-old mark and beyond.

PITCHf/x reports movement in horizontal and vertical vectors. Horizontal movement (Hmov) is the right or left movement of the pitch compared to the expected trajectory without air resistance. A positive value is away from a right-handed batter. Vertical movement (Vmov) is the amount the ball moves up or down relative to the expected drop in a vacuum. A positive value means the ball dropped less than would be expected without effective spin.

It has been established that fastball velocity tends to decrease with age, but movement trends haven’t been looked at before. Might aging pitchers compensate their decrease in velocity with an increase in movement? Or does time steal away effective spin as well?

Let’s find out.

Methods:

I collected all PITCHf/x data from every pitcher with at least 300 innings pitched from 2007 to 2018 (n=537). Data was aged based on the age of the player on April 1st of the corresponding season. Velocity, horizontal movement, and vertical movement were averaged for each age and graphed. The horizontal axis of left-handed pitchers was flipped so right and left-handed data could be analyzed together.

I then took out the top starters by WAR (n=63), according to FanGraphs, from 2007 to 2018 and graphed their data separately.

Results/Discussion: Graphs are available by clicking on the links below, and raw data available in tables at the end of this post.

Four-seam, Overall

Velocity reaches its peak at age 21, then it declines at a pretty constant rate for a couple decades until falling off the table at 39.

Horizontal movement reaches a value of around -5 inches and stays very constant until the age of 38, where the number of subjects decreases quite a bit, leading to increases in year-to-year variability.

Vertical movement stays extraordinarily constant throughout the ages of 19-44.

Curveball, Overall

Velocity declines over time, for the most part, although not as predictably as the fastball.

Horizontal movement actually decreases from ages 19-24, then remains fairly constant until the n values get low after ages 39 and above.

Vertical movement shows similar trends to horizontal, actually decreasing for five years, then remaining fairly constant, and then getting unpredictable.

Slider, Overall

Velocity, unlike the fastball, initially increases for five years, reaching its peak at age 24, then pretty constantly decreases for the remainder of years.

Horizontal movement finds its value around the age of 21, and, if you squint, you could convince yourself there is an upward trend from the age of 24-39.

Vertical movement stayed around +3.5 inches and didn’t show any clear trend until the age of 39.

Conclusion:

The real bulk of data was between the years of 22-39. It’s difficult to draw any conclusions from data outside this age range, as the n values drop off significantly. From what I can tell, the major predictable trend is a decline in velocity with age. Movement appears very consistent in the four-seam, and no clear trend emerges with the curve or slider. The lone exception may be a slight trend toward more positive horizontal movement in the slider with respect to age.

This is mildly surprising, particularly with respect to the four-seam. It seems as pitchers lose their ability to throw hard, their ability to apply effective spin stays the same.

I thought movement may increase with age before decreasing before the end of a player’s career to explain a plateau in pitching performance in a player’s “prime.” But movement doesn’t seem to change appreciably. Again, maybe there was a trend upward with slider horizontal movement, but I’d be hard-pressed to call this clinically significant. I was expecting movement in the breaking pitches to increase with age, at least until the age of 30, but this was pretty definitively not the case.

Bill Petti showed in a previous FanGraphs post in 2012 that as velocity predictably decreases from the age of 21 on for starting pitchers, performance stays more or less consistent until age 28-29 when trends in K/9, BB/9, HR/9 etc. can be clearly seen to deviate from the early career baseline. With relievers, however, performance metrics deteriorated almost immediately, along with velocity.

Perhaps the movement increases with age to compensate for decreasing velocity are restricted to the best starters, and this is why their performance metrics stay pretty constant until they turn 30. If any improvement in movement is seen to counter losses in velocity, it would be in the starters who have provided the most value in their career.

Starter graphs (click to view): Four-seamers | Curveballs | Sliders

Looking at the data for the top starters by WAR (n=63), we see the expected trend in velocity in all pitches. The four-seam showed a trend toward less horizontal movement (toward 0, less run), which is the opposite of what I was looking for. There was no obvious trend in Vmov to my eye.

I could convince myself that there is a trend toward more horizontal movement in the curve, but the important vector for the curve, Vmov, shows a trend toward less drop.

Likewise with the slider, there is no clear trend in its important vector, the Hmov. However, there is a trend toward more positive Vmov (meaning it resists gravity more). Again, this was not what I was expecting. Overall it seems pretty clear that breaking pitches are not getting better to compensate for a drop in velocity.

It seems that velocity isn’t everything and neither is movement. In other words, “stuff” is not the be-all-end-all of the best pitchers. It seems the pitchers who provide the most value and have the most longevity are not those whose talents last the longest, but those who make the most of what they have, even while it is leaving them.

Starter Data: