Going Deep: Bauer Units With Four-seam Fastballs

(Photo by George Walker/Icon Sportswire)

Last month I wrote about curveball spin rates and context using Bauer Units, a measurement created by Driveline Baseball, where I looked at using spin rate in tandem with velocity to create effective curveball movement. In this article, I’ll investigate the Bauer Unit score of four-seam fastball pitchers, look into their location tendencies, and evaluate their effectiveness in terms of what their BUs tell us about their pitch.

Before I begin, I must point out that some of this data was mined a week or so ago and there may be minimal variance in some of the numbers I present. In general, we aren’t concerned with comparing real-time stats, rather just looking into samples. Also, I chose four-seam fastballs as other variants of the fastball category tend to be more volatile because of their (heavier) movement.

To begin, I found pitchers that have thrown at least 1000 four-seam fastballs in 2018. From there, I extracted the average velocity and spin rate of their four-seam fastballs and found their BU ’score’. How do you find a pitcher’s BU score? Its simple– divide the spin rate by velocity; that’s it! Chart 1 shows the pitchers involved in this research.

While we’re at it, lets put some context to these BU scores. In the sample group I formed, the average BU score was 24.3 with a 1.5 standard deviation. In an article written by Driveline Baseball Associate Researcher Michael O’Connell, he discovered that high spin pitchers tend to have higher BU scores but velocity has no correlation to BU score (both rung true when I ran my numbers). To summarize the latter, here is a quote from O’Connell:

This can help clear up some confusion when you are looking at pitchers who throw high 90s with spin rates in the 2300 range. Technically 2300 rpm is above the average of 2200, but with velocity taken into account, they are actually below average.

In terms of BU score, velocity and spin rate depend on each other. This is the case because you are able to use spin rate and BU score to help recognize how to best use your four-seam fastball with how hard you’re throwing the pitch; spin rate tends to be a bit more unstable than velocity.

It must be noted that the subsequent info is generally more applicable to younger pitchers (high school, college, or even minor leagues) but can also be useful if you have a pitcher who suddenly isn’t doing well when it comes to his fastball.  Habitually, you’ll want to follow these rules–If you have a higher than average BU score, it is suggested that you keep your fastball middle/up in the strike zone. If you have a lower than average score, the pitcher would do well to keep his fastball lower in the zone. If you’re league average, it might be a good idea to develop a two-seamer. Why? Because you’re not getting great movement. Simply throwing hard with a spin rate that parallels results in minimal movement (recall Magnus Force) that is easy to key in on.

Let’s get started. Below are three of the low-end BU scores followed by several in the middle that resides near the mean, and three on the high end. Additionally, I displayed the Pitch Info value per 100 pitches represented by wFA/C and the Pitch IQ (a la Brooks Baseball) movement values; think of 100 being league average movement. All numbers are based upon four-seam fastballs only.

For my low-end sample, I selected Reynaldo Lopez of the Chicago White Sox. Lopez uses his fastball at a rate second only to Justin Verlander (more on him later) and has below average movement on his four-seamer. Hitters facing Lopez produce league average BAA and whiff rate. Referencing the feedback on BU scores, I created a few tables to expand upon what our sample pitchers do with their fastball. As Lopez is on the lower end of the BU score, I took some data on his middle/low zone pitches (to include out of the zone pitches). We see total fastballs thrown followed by how many are thrown low (with rate), how many are called or swung at strikes (with rate), and pitches in and out of the zone with the ratio of pitches (in divided by out of the zone). This will be the basis of all subsequent pitchers I review.

Lopez doesn’t seem to attack low zone very often (one out of every three pitches) and when he does, he’s not very successful. We have a decent sample of low fastballs and it’s hard to say if he’d do much better if he threw lower in the zone more consistently. So, conversely, how well does Lopez’s fastball perform high in the zone? A .250 BBA. Interesting; Lopez would seem to be an exception to the rule.

Moving on, we’re going to review the middle of the pack; league average BU four-seam pitchers.

Some pretty prominent names on this list but just Luis Severino and Gerrit Cole break the 50% mark on four-seam usage. We’ll use those two as our samples as we have a few extra on this list. Chart 5 is a little different as the average BU pitchers don’t really have a location that is preferred; it was suggested they work on a two-seam fastball as there is too much room for error. So, I’ve broken the two pitchers down between high/low zone. When you see a ‘/’ it measures both locations. The other stats are figures that cover the entire area in and out of the zone.

We can see that Severino (top) pitches better throwing low in the zone but his overall BAA on his four-seam is not very good at all. Severino also has one of the highest ratios of in the zone versus out of the zone; for every 1.54 pitches IZ, he throws one OOZ. This, however, could be indicative of a much larger problem as hitters are really attacking the strikes he throws and succeeding. This is a reason that BUs suggest developing a different type of fastball. Going back to Chart 4, it shows Severino has pretty much league-average movement on his fastball (HMov/VMov). Here, we have more the rule than the exception.

Cole (bottom) is a little different; he has below average movement but still succeeds especially low in the zone. He’s also a little more balanced on his IZ/OOZ ratio.

Lastly, let’s look at the pitchers on the high end of the BU score.

As I pointed out earlier, Verlander has very high four-seam fastball usage as well as great numbers to legitimize. So does Verlander play by the BU score rules?

It appears that he does for the most part. Just over half of all his four-seam fastballs sit high in the strike zone. The pitch garners a strike in one out of every four pitches and he balances in/out of the zone placement well. The Houston Astros pitching staff as a whole, along with the St. Louis Cardinals, understand the importance of attacking high in the zone; effective velocity principals that will be touched on in a future article.

Of course, it’s very hard to put much stock in this evaluation. Mainly because we don’t know what circumstances the four-seam fastball is being used; sequence, count, score, runners on base, batter handedness, etc. But the principal of BUs is applicable regardless. Knowing the pitcher’s BU score is helpful because we can attempt to enforce certain tendencies for a pitcher to use his velocity and spin rate to be the most effective he can be. Bauer Units are a great tool to do that but its hard to quantify because pitchers change what they throw (and when) as well as what (sequence, location) is working for them on a particular day.