Revisiting the Cardinals’ spin rate data

We’re now three weeks into MLB’s new enforcement policy regarding pitchers’ use of foreign substances. Of course, these developments are at least partially the result of Mike Shildt forcing the league’s hand with his press conference following Giovanny Gallegos Hatgate.

“Is our house 100% clean? I certainly hope so,” Shildt said in the aforementioned presser. “Am I creating more of an opportunity—because I just spoke to our pitchers—am I creating more awareness to our group? Potentially.”

I think the working assumption among Cardinals fans was that St. Louis’ pitching staff had to be at least relatively ‘clean’ for Shildt to go public with his remarks like he did. While we can’t arrive at definitive conclusions, analyzing changes in spin rate data from before/after June 21, the day pitcher inspections began, provides valuable pieces of information. Evaluating pitchers (especially as the trade deadline nears) is already a complex task; determining the potential effects of sticky stuff adds yet another layer.

With that in mind, let’s hone in on the Cardinals. J.P. Hill previously explored year-to-year trends in spin rate, and we can now begin to supplement that data by seeing what changes have occurred within 2021 under the enforcement guidelines. I included pitchers who threw at least five of a specific pitch type both before and after June 21st, which prompts an obligatory small sample size disclaimer. Another reminder: a decrease in spin rate in and of itself doesn’t prove much. To give the graphs and data table below a bit more context, Eno Sarris and Brittany Ghiroli wrote at the Athletic last month that “one standard deviation of change within a season for a single pitcher is 115 revolutions per minute.” In addition to individual metrics, you’ll also find the average spin rates for Cardinals in the sample as well as the overall MLB numbers for that pitch type.

I don’t know about you, but my first reaction when combing through the data was yikes, Alex Reyes. His 2021 peripherals were already concerning (3.50 FIP, 4.42 xFIP, 4.45 DRA) and a recent drop-off in spin rate doesn’t inspire confidence either. His velocity doesn’t appear to have changed significantly during the same timeframe. Curiously enough, if we dive deeper into the small sample size pool, Reyes’ FIP (3.80 to 2.32) and xFIP (4.57 to 3.81) have actually improved since June 21st, led by a much lower walk rate (20.6% to 8.6%) to compensate for a reduced strikeout rate (32.6% to 22.9%).

Other Cardinals with noteworthy spin rate declines (for navigation ease, I’d reccomend using the search bar at the top of the table) are Jake Woodford, Giovanny Gallegos, Seth Elledge, Carlos Martínez and Johan Oviedo. Some, like Kwang Hyun Kim and Adam Wainwright (the latter admitting to doctoring baseballs in 2019, but implying he hasn’t since), also have lower spin rates on various pitches, but with more modest decreases. Then there are pitchers with virtually no change, if not slight increases. An example of this is John Gant, whose higher four-seam and curveball spin rates might be explained by his transition from the rotation to the bullpen.

Like I said earlier, I’m not going to try to use this data to confirm or deny anything. Other factors like nagging injuries can also affect spin rate, so apporach these numbers however you please. One thing that is certain is this: spin rates are down across the board, and MLB’s latest enforcement efforts are presumably having a nonzero effect.