Trevor Bauer is one of baseball’s most interesting players. You may know him from his warm up routine:
or from this incident.
These are some quite entertaining moments, but there is a lot more to Trevor Bauer than meets the eye. He is a pioneer in baseball’s analytics revolution and has been using sabermetrics to improve his performance throughout his career. As an outspoken mad scientist in the baseball world, Bauer undoubtedly follows and investigates the improvements of his peers to improve on his own game. Which is why, upon stumbling across the universal improvement of the Astros pitching staff’s spin rate, Bauer likely ran a risky experiment this past season to see if he experienced a similar result to the rest of the Astros.
Bauer has been very outspoken about pitchers using foreign substances such as pine tar, which has been proven to increase a pitcher’s natural spin rate as well as improve movement on breaking balls. In 2018, Bauer tweeted out a message saying,
“If only there was just a really quick way to increase spin rate. Like what if you could trade for a player knowing that you could bump his spin rate a couple hundred rpm overnight...imagine the steals you could get on the trade market! If only that existed…”
This tweet was targeted towards several pitchers on the Houston Astros, who all saw a significant increase in their average fastball spin rates (as well as other pitches) while playing for the Astros. Perhaps a more suspicious indication of these Astros players using substances was the minimal increase in pitch velocity, which has been proven to have a direct correlation with spin rate (meaning spin rate should go up as velocity goes up). Take Gerrit Cole, for example. Through his 2015 to 2017 seasons on the Pirates (Statcast began tracking spin rate in 2015), Cole's average fastball spin rates by season were as follows: 2156 rpm, 2183 rpm, 2164 rpm. As soon as he was traded to the Astros in 2018, his average fastball spin rate magically increased to 2379 rpm. It then increased even higher in 2019, up to 2530 rpm. This occurred with a minimal 0.6 mph increase to Cole’s average fastball velocity from 2017 to 2018 (his average fastball velocity again increased just 0.6 mph from 2018 to 2019). The reason this is so abnormal is because every pitcher has a natural spin rate/fingerprint. In the book The MVP Machine written by Ben Lindbergh and Travis Sawchik, it states that
"According to those most familiar with the nature of spin—Driveline Baseball researchers, Bauer, and perhaps University of Illinois physics professor Alan Nathan, an MLB consultant—such a sizeable increase is unlikely to occur naturally with such consistent velocity. 'It’s probably pretty hard to change that [fastball spin] ratio for an individual,' Nathan told FiveThirtyEight. 'A fastball is pure power. There is no finesse.' While spin increases with velocity, Driveline discovered that pitchers have natural rpm/mph fingerprints, which they dubbed Bauer Units in order to normalize and compare pitches and performance... The only method that Bauer and Kyle Boddy identified of increasing rpm/mph rates on a fastball was applying a sticky substance to a pitcher’s hand or ball to improve the pitcher’s grip, thereby increasing spin."
You get the point. This isn’t an article about the Houston Astros cheating with foreign substances, so I won’t be listing out more drastic spin rate changes; however, I will continue to talk about Gerrit Cole, who also is no longer with the Astros (whose spin rate, if my theory is correct, should decline in this upcoming season).
Bauer and Cole have had a long history. The former UCLA teammates were fierce rivals in college with Cole supposedly telling Bauer that he had no future in baseball and insulting his work ethic as a freshman. Later, after Cole was traded to the Astros in 2018, Bauer began to beef with Astros players and the organization as a whole. During that time, Bauer likely noticed that in 2018 Cole saw a 215 rpm increase in his average fastball spin rate out of nowhere, which is why he tweeted about the Astros likely using foreign substances. Bauer, on the other hand, only saw his RPM increase 97 RPM on his average fastball spin rate across a span of four years (from 2225 rpm in 2015 to 2322 rpm in 2018), most likely frustrating him due to his lack of improvement in comparison to other star pitchers. Now, I want you to look at this histogram of the spin rate of every fastball Bauer threw in 2019.
Interestingly, a portion of Bauer’s fastballs somehow had significantly higher spin rates in comparison to the majority of his fastballs. It looks just like what happens when pitchers use foreign substances. You may be thinking that this makes Trevor Bauer a cheater too. Right? Wrong. This portion of increased average fastball spin rates was part of Bauer’s spin rate experiment. From this graph, you see a jump in Bauer’s fastball spin rate starting from his start on 9/4/2019 all the way until his final start on 9/22/2019.
Prior to September, Bauer’s average spin rate was at 2358 rpm. During the month of September, Bauer’s average spin rate suddenly jumped to 2757 rpm, a whopping 399 rpm increase (p < 2.2*10^-16, Welch’s t-test). The Reds weren’t in playoff contention during September, so Bauer’s starts were likely meant to be an experiment to prove that foreign substances can in fact drastically increase natural spin rate, and, for the most part, go unnoticed when using it. However, how did we come to believe that Bauer was using substances to increase his spin rate?
Looking at the first histogram below, we see that prior to September, the majority of Bauer’s fastballs were around 2100 to 2600 rpm in spin rate with minimal outliers. Then looking at the second histogram, in September, Bauer’s average fastball spin rate spiked, with a majority of his fastballs falling in the 2600 rpm to 2900 rpm range.
This jump being so clear and clean indicates that Bauer did use some form of foreign substances. It is impossible to get such a dramatic increase in spin rate, something that is natural to each person, in the span of 5 days (Bauer’s last pre-September start was on 8/31/2019) without the use of foreign substances. In addition, Bauer’s average fastball velocity during September was 93.62 mph, which, surprisingly, is lower in comparison to the other months of the season in which his fastball averaged 94.48 mph. As I mentioned earlier, there is a direct correlation between pitch velocity and spin rate, meaning that Bauer’s spin rate, hypothetically, should have actually decreased, which it did not.
I have been obsessing over spin rate throughout this entire article, but why is it so important?
This chart, courtesy of Jeff Zimmerman, shows how the velocity and spin rate of a pitch can influence how likely a hitter is to swing and miss. For the most part, as spin rate increases, swinging strike percentage also increases.
If we look at 2017 Gerrit Cole, his fastball averaged at 95.9 mph with an average spin rate of 2164 rpm, placing him at around an estimated 7.4% to 8.9% swinging strike percentage. Now, when we look at 2018 Gerrit Cole, the year he got traded to the Astros, his fastball was similar in average velocity at 96.5 mph, but his average spin rate jumped up to 2379 rpm, putting him in the 9.3% to 10.2% swing strike percentage range. 2019 Gerrit Cole (97.1 average velo and 2530 rpm average spin rate) fell in the 12.8% to 13.6% range. When we look at Cole’s real life swinging strike percentage on all his pitches, which should be higher than just his fastball swinging strike percentage, from 2017 to 2019, it goes as follows: 9.5%, 14.1%, 16.8% (a career high). His strikeout percentage and strikeouts from 2017 to 2019 goes as follows: 23.1% and 196 Ks, 34.5% and 276 Ks, 39.9% and 326 Ks (both a career high). A simple increase in Cole’s spin rate has transformed him from a decent starter on the Pirates to a strikeout machine that is embarrassing some of the best hitters in the league.
Bauer, in my opinion, ran this spin rate experiment to show baseball fans how Gerrit Cole became the monster that he is today. This was the first time in Bauer’s career that the entire month of September barely mattered because the Reds had no shot at the playoffs at this point while the Indians often did, meaning that even if Bauer got suspended for a few games it wouldn’t have that big of an effect. Bauer wanted to use his September outings to prove that Cole’s dominance wasn’t some secret that the Astros have in regards to pitcher development but instead, good old sticky stuff that bumped Cole’s spin rate up a couple hundred rpms. Bauer’s pre-September fastball pitch data, 94.48 mph average velocity and 2358 rpm average spin rate, places him in the 7.9% to 8.5% range. Bauer's actual fastball swinging strike percentage, including his 4-seam, 2-seam, and cutter, prior to September was 10.08%. With Bauer’s increased spin rate of 2757 rpm during September, his predicted swinging strike percentage goes off the charts. Bauer's actual fastball swinging strike percentage during September jumped to 12.75%, a 2.7% increase.
Data courtesy of Baseball Savant and Fangraphs
Graphs were created by Henry Jia using R
Disclaimer: There has been suspicion about Gerrit Cole using foreign substances, but there has been no real proof that he does. However, it has been revealed that many MLB pitchers do in fact use foreign substances, mostly pine tar and Pelican Grip Dip, to improve spin rate and pitch break. Many hitters have not been bothered by this mainly because these foreign substances also give pitchers more command meaning less hit by pitches. Looking at the numbers, Cole’s spin rate increase is very suspicious, but I do not have solid evidence to prove that he is indeed cheating. It is only mine and Trevor Bauer’s suspicions (the Astros are known to be cheaters though…so who knows).