Bauer Units

In November 2016 the Bauer Unit was born. Named after Trevor Bauer, it is defined as spin rate divided by pitch velocity. For years, Trevor Bauer experimented to find ways to pitch better. His recent controversial thoughts were about increasing spin rate by a variety of sticky substances. Let’s save that discussion for another time and place.

Looking at spin rate did not fully explain why some pitchers had better results. Travis Sawchick best stated the importance of the Bauer Unit, “Raw spin rate generally increases with velocity, but it’s the spin-to-velocity (rpm-to-mph) ratio that is so crucial to determining pitch movement.” Pitch movement is directly related to pitch results. One reason is that missing the sweet spot on the bat by an inch makes a huge difference.

Bauer Units do not tell the whole story of pitch movement for three reasons:

• Statcast’s measure of spin does not separate transverse spin (creates movement) and gyro spin.
• Each pitcher can have a different spin axis, which greatly changes pitch movement. Two ways to change spin axis are 1) change arm angle, and 2) push to the side of the ball as it is released.
• Pitchers can design pitches in many ways, such as grip, wrist angle, pressure on fingers, and thumb position.

Fastballs are fast. They seem to defy gravity because of their backspin. Cutters and sliders are slower with different spins causing different movements. The combination of pitches makes hitting a challenge. Often pitchers have a repertory of pitches that includes fastball and either cutter or slider. These three pitches cover a lot of territory (see picture).

Makakilo

Most Diamondback starting pitchers, including Madison Bumgarner, Zac Gallen, Luke Weaver, Merrill Kelly, and Alex Young, had the cutter in their arsenal to complement their fastball. Those who instead had the slider in their arsenal include Caleb Smith, Taylor Clarke, and Robbie Ray.

Which Diamondbacks have the highest Bauer numbers? In 2020, for the 4-seam fastball, it’s good news that 13 Diamondback pitchers (8 starters and 5 relievers) had Bauer Units above the average in the Majors. The better question is how many of those pitchers had a complimentary pitch (either slider or cutter) that was also above average in the Majors (20 pitch minimum)? Four. Details are shown in the following chart:

Data from Baseball Savant. 2020 season.

Caleb Smith has star potential that was not in evidence in my previous article about projected ERAs. In 2020, he hugely increased the spin rate on his slider from 2297 rpm to 2526 rpm. As a result, his slider whiff rate increased from 31% to 46.2%. For the Diamondbacks, his overall ERA was 2.45.

At the end of the 2020 season, Madison Bumgarner showed he has what it takes to return to his status as an ace. In September, excluding a game against the Angels, his ERA was 2.53.

Honorable mentions are made of two relievers:

• Keury Mella whose 4-seam fastball averaged 23.1 Bauer units, and slider averaged 29.5 Bauer Units. Slightly below average Bauer Units on his fastball kept him off the chart.
• Jeremy Beasley whose four-seam fastball pitches averaged 25.8 Bauer Units and sliders averaged 29.6 Bauer Units. Small sample size (10 total pitches) kept him off the chart.

How do the Diamondbacks’ 4-seam fastballs, sliders, and cutters compare to the average of all teams? An initial look at Bauer Units mistakenly showed that the slider compared poorly. A deeper look at wOBA and K% showed results from the slider were better than the other two pitches, and better than the averages in the Majors. Clearly, the Diamondback sliders were extraordinary.

The 4-seam fastball and the cutter are knocking on the door because their Bauer numbers exceed the league averages. For 2020, the following chart summarizes the comparison of Bauer Units, wOBA, and K%.

Data from Baseball Savant. 2020 season.