Antonio Senzatela has a pretty crummy four seam fastball. Well, by the general populace he certainly doesn’t--it’s a pitch that sits in the mid 90s and tops out at around 98 mph. I couldn’t hit it in a thousand tries, and most likely neither could you. But by the standards of major league fastballs, it lacks most of the positive traits that make four seam fastballs hard to hit. Senzatela’s fastball has always had good velocity, but a combination of low and very ineffective fastball spin has put his fastball at the bottom of the leaderboards in vertical movement. With that lack of fastball carry has also come an inability to miss bats.

Season	Velocity (MPH)	Spin Rate (RPM)	Active Spin	Vertical Movement (in.)	Whiff Rate
2017	94.3	2150	N/A	14.95” Up	13.5%
2018	93.6	2087	N/A	11.81” Up	12.3%
2019	93.7	2101	61.8%	11.03” Up	13.0%
2020	94.3	2144	61.2%	10.62” Up	11.5%

Among pitchers who have thrown 1000 or more four seam fastballs since 2017, only Jordan Zimmermann has a lower whiff rate on that pitch than Senzatela. However, take a look at the vertical movement on his fastball in 2017. That’s still a below average amount of four seamer rise, but it’s definitely preferable to the extremely low vertical movement that Senzatela’s been getting the past three seasons. So where did this fastball carry go, and can Senzatela get it back?

The first theory I had to explain such a dramatic drop in vertical movement on Antonio Senzatela’s four seamer was that he simply just threw a more spin efficient fastball in his rookie season. As previously mentioned, Senzatela’s fastball has very poor spin efficiency; it’s been in the 4th percentile of active fastball spin in 2019 and 2020. While we don’t have publicly available active spin data for the 2017 and 2018 seasons, we do know that, in addition to a lack of carry, fastballs with heavy gyro spin also tend to generate less armside run. So, how has Senzatela’s horizontal fastball movement trended in his career?

Season	Horizontal Movement (in.)	Spin Axis
2017	3.6” Right	12:27
2018	4.41” Right	12:49
2019	4.98” Right	12:55
2020	5.88” Right	1:05

Hmmm, so Antonio Senzatela has generated more run on his four-seamer in each successive season as a major leaguer. Note the shift in spin axis here and how it’s correlating with armside run; as a fastball’s spin axis gets further away from 12:00, it trades backspin driven vertical rise for sidespin driven horizontal run. Senzatela, who already had a high ground ball rate with his bat-finding fastball, may have just decided to alter his fastball towards catering to its strengths--rather than seeing if he could improve its weaknesses. It’s also important to note that Senzatela is not the only Rockies starter that has trouble generating swings and misses on their four-seamer.

4S Whiff Rate By Season	Jon Gray	German Marquez	Kyle Freeland	Rockies	League
2017	12.6%	16.4%	15.2%	16.3%	19.8%
2018	17.4%	18.5%	13.6%	17.2%	20.7%
2019	12.0%	15.3%	12.0%	16.6%	21.8%
2020	12.7%	15.1%	11.7%	15.0%	22.6%

None of the core Rockies starters over the past four seasons have been able to elicit whiffs on their four-seamer, and the Rockies as a whole placed dead last in four seam fastball whiff rate in 2017, 2019 and 2020 (they were 28th in the high watermark 2018 season). This doesn’t really come as a big surprise; a Fangraphs Community piece by Adam Maahs, focused on pitch movement at and away from Coors in the 2017 and 2018 seasons, observed an average three-inch drop in four-seam vertical movement and a two-inch loss in four-seam fastball horizontal run.

Additionally, while doing research for this piece I observed that many Rockies starters also experienced a similar drop in fastball carry from 2017 to 2018. Since most of the home and away splits for these core Rockies starters’ fastball movement in the past four years share that same reduction in vertical movement, it’s hard to answer this question of lost fastball carry as it pertains specifically to Senzatela. What started out as a seeming individual anomalous result has affected the Rockies’ pitching as a whole, and that diagnosis necessitates a more complex study than what is delved into here.

However, there are some changes that Senzatela made in 2020 that bode well for successful outcomes in the future. In 2019, Senzatela’s four seam fastball was a mess. It didn’t move and was often center cut, leading to the pitch being 17.0 runs below average--according to Pitch Info. In 2020, Senzatela’s fastball was a much more palatable 0.7 runs above average, despite retaining the same spin and movement traits that plagued his fastball in 2019. A lot of that change can be credited to better command and an increase in armside run, with Senzatela locating the pitch more towards the inner third to right-handed batters. Mechanically, the most notable difference is Senzatela lowering his arm slot when throwing the fastball.

Season	Vertical Release Point (ft.)	Horizontal Release Point (ft.)
2017	5.99’ Up	2.30’ Right
2018	5.95’ Up	2.29’ Right
2019	6.13’ Up	2.34’ Right
2020	5.83’ Up	2.58’ Right

Lowering the armslot helps to create a sharper vertical approach angle for four-seam fastballs, and while that hasn’t translated to more whiffs for Senzatela in 2020, it did help him get some fastballs on the armside black and bring his hard hit rate back to career norms. Additionally, Senzatela’s fastball usage was a career low 56% in 2020, while his slider usage was a career high 24%. Any reduction in four-seam fastball usage is a plus for a pitcher that makes half of his starts at the movement-killing pitching environment of Coors Field.

While I’m not sure that Senzatela is going to find the carry on his fastball that he and many other Rockies pitchers seemingly lost in 2018, he’s making adjustments that should make the pitch as effective as it can be. Senzatela, when he’s right, is a nice back of the rotation piece that uses his fastball, breakers and an occasional change to avoid hard contact and get the ball on the ground. Changing his mechanics to better locate his fastball and relying more on the slider are encouraging developments that should enable Senzatela to continue rebounding from a disastrous 2019. That’s not a sexy profile, but a usable rotation piece in year one of arbitration control is something the Rockies shouldn’t pass up.

Credit: Baseball Savant for movement, spin rate, active spin rate, velocity, whiff rate, and release point data. Brooks Baseball for spin axis data. Fangraphs for heatmaps and Adam Maahs for Coors pitch movement research.