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Players frequently enter spring training in, "the best shape of their lives," but offseason programs rarely seem to pay significant dividends. The extended offseason may have provided some players with the opportunity to make unusually significant adjustments this year, though.
One example of such an adjustment is Yankees starting pitcher James Paxton, who recently announced that he’s been working to add spin to his fastball. Although it's impossible to say exactly how much Paxton's spin rate will increase this season, spin rate increases have helped unlock a new level of performance for some pitchers.
Most notably, Gerrit Cole owes a large part of his impressive breakout to a spin rate increase. Similarly, Lucas Giolito benefited from a higher-spin fastball last year. While an increased spin rate would sound like a positive attribute for Paxton as well, how much should fantasy owners care?
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Taking the Heater for a Spin
As a baseline, here’s how Paxton’s fastball performed last year:
| Usage % | Spin Rate (RPM) | SwStr% | xwOBA |
| 53 | 2263 | 11 | 0.335 |
To understand how Paxton’s performance might change as a result of his increased fastball spin, it’s important to know how much his spin rate is likely to increase. 16 qualified pitchers increased their fastball spin rates last season, with the increases ranging from just 1 RPM to 234 RPM.
| Name | 2018 FB Spin | 2019 FB Spin | Increase |
| Lucas Giolito | 2099 | 2333 | 234 |
| Gerrit Cole | 2379 | 2530 | 151 |
| Matthew Boyd | 2282 | 2384 | 102 |
| Trevor Bauer | 2322 | 2415 | 93 |
| Julio Teheran | 2326 | 2400 | 74 |
| Jakob Junis | 2024 | 2079 | 55 |
| Aaron Nola | 2116 | 2171 | 55 |
| Tanner Roark | 2103 | 2145 | 42 |
| Dylan Bundy | 2417 | 2458 | 41 |
| Zack Wheeler | 2312 | 2341 | 29 |
| Jacob deGrom | 2362 | 2388 | 26 |
| Jon Lester | 2230 | 2251 | 21 |
| Charlie Morton | 2243 | 2259 | 16 |
| Patrick Corbin | 2267 | 2283 | 16 |
| Mike Fiers | 2309 | 2322 | 13 |
| Rick Porcello | 2433 | 2434 | 1 |
When discussing his grip change in an interview with YES Network, Paxton said that he’s seen “good results” as he works to increase his spin rate. Every 100 RPM change in spin rate affects movement, so it seems fair to expect Paxton to have increased his spin rate by at least 100 RPM.
Only Lucas Giolito increased his fastball spin rate by more than 200 RPM last season though, so it would be optimistic to expect Paxton’s spin rate to increase by that amount. As a result, an estimate of a 100 RPM increase in Paxton’s fastball spin is reasonable, taking his average spin rate from 2263 RPM to 2363 RPM.
What Would an RPM Boost Do For Paxton’s Fantasy Value?
Last season, Trevor Bauer (93 RPM increase), Matthew Boyd (102 RPM increase), and Gerrit Cole (151 RPM increase) saw their fastball’s swinging-strike rates increase by 2.7 points on average. That’s an admittedly small sample size, but the implications are in-line with Driveline research on fastball spin and its relationship to swinging-strike rates.
Since Paxton’s fastball posted an 11% swinging- strike rate last year and a 12% swinging-strike rate the year before, let’s assume that with an increased spin-rate its swinging-strike rate would jump to 13% in 2020. Based on last season’s fastball usage and effectiveness, that increase translates to an increase in his overall swinging-strike rate by about 0.5 points.
A pitcher’s swinging-strike rate correlates strongly with his strikeout rate, and a 0.5 point increase in Paxton’s swinging-strike rate last season would result in an implied increase in his strikeout rate to 31.8%. If all of Paxton’s other numbers remained the same, his FIP would have decreased from 3.86 to 3.77.
Fantasy owners shouldn’t put too much weight on Paxton’s offseason spin-related adjustments then, but a 0.09 change in FIP undersells the potential benefit of the adjustments. Although it would be an optimistic projection, Paxton could reasonably see his fastball’s swinging-strike rate rise to 14% in 2020. If Paxton's fastball posted a 14% swinging-strike rate last year, then his FIP would have fallen to 3.63. A 23-point positive change in year-over-year FIP would have ranked eighth among pitchers with at least 150 innings last year, underscoring the potential upside of Paxton’s adjustments.
Conclusion
Paxton’s ADP since the start of April is about 120, making it around 10 to 15 picks too low given his adjustment-related upside. For fantasy owners who pass on drafting Paxton this year due to injury concerns, his early-season fastball spin-rate should be closely monitored. If Paxton’s fastball spin rate flirts with 2500 RPM in his first start or two, then he should be a priority early-season trade target.
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