In an arsenal that he’s frequently changed, Sonny Gray’s curveball remains largely the same. It’s still the 79-81 mph hard curveball he employed when he debuted for the Oakland Athletics in 2013. Although he’s used it less this season than in years past, Gray still feels a strong connection to the pitch.
He described it as his “bread and butter pitch” during an interview with Rob Friedman in May. He throws it in many ways. The pitch induces chases (78th percentile chase rate), swing and misses (64th percentile swinging strike rate), and can succeed in the zone (83rd percentile zone rate).
Part of why Gray is so comfortable with his curveball has to do with what feels comfortable anatomically.
Some pitchers excel at “staying behind” the ball, meaning their hand is literally behind the ball as they release the pitch. Others prefer “being on the outside,” while the rest “stay on the inside.”
There are five muscles in the arm that work to pronate or supinate the hand. The appropriately named supinator acts in tandem with the biceps brachii to supinate, while the also appropriately named pronator teres, pronator quadratus, and flexor carpi radialis. Because of what feels best for his body, Gray is more inclined to use the former two.
Even when visualizing “pulling [his two-seamer] straight down,” Gray’s hand is slightly supinated.
Gray’s so-called supination bias means his hand is most comfortable on “the outside” of the ball with the back of his hand facing the right. That’s the position that players throw curveballs with, in addition to many other pitches, like sliders and cutters. It’s also true that two-seamers and changeups work well with supination due to seam-shifted wake, even though they move armside (right).
Utilizing his natural hand position, Gray lets seam-shifted wake carry his two-seamer in a way that does not disrupt his other supination-based pitches. He points the white of the horseshoe at the batter when throwing his two-seamer, while the spin direction of the pitch is somewhere between 1 o’clock and 2 o’clock. Forcing the white spot of the ball to lead the way with one seam slightly ahead on one side than the other will create an imbalance in the wake the ball creates. One side will experience turbulent, rough flow, while the other will experience laminar, smooth flow. That causes the turbulent side to “catch,” pulling the other more smooth flow and thereby creating more sideways movement.
As I mentioned in this article about Dallas Keuchel, you can crudely measure the amount of seam-shifted wake on a pitch by using BaseballSavant’s Spin Direction section. You can infer this by looking at the difference between spin-based movement and observed movement (this is called 2D Axis Differentiation by Driveline Baseball). An hour difference is considered a lot. Gray throws with 1 hour and 15 minutes of difference on his two-seamer, or 45 degrees of 2D Axis Differentiation.
Gray’s supination bias hasn’t always been celebrated by coaches and teams in his career. During his time with the New York Yankees, he became aware of the exceptionally high raw spin of his four-seamer. At the time, pitchers across the league dabbled with their own high-spin fastballs to much success. It made sense for the Yankees, wishing to help Gray follow in the footsteps the way the Houston Astros helped Justin Verlander and Gerrit Cole reach their fullest potential.
By unlocking their high spin by throwing them up in the zone, pitchers who have neither a supination nor pronation bias are predisposed to succeed in this way. High active spin rates, meaning spin that follows the direction of the pitch, lead to the rising fastballs that have dominated pitching for years.
Gray was encouraged to throw his four-seamer high, only for its natural cut action (only 68% active spin on the pitch this season) that stems from his supination bias to minimize the amount of carry the pitch had. Instead of the ball missing barrels, it too often dropped right into barrels. It wasn’t until he moved on from New York that he truly unleashed his natural abilities.
He continues to find ways to let his natural ability shine.
Gray used to throw a changeup ~5-10% of the time to begin his career. In 2022, his first season with the Twins, it vanished. Rather than pronating the pitch and “throwing the circle at home plate,” he’s begun throwing the pitch “just like [his] two-seamer.” Leaning into his seam-shifted wake skills, Gray’s circle-changeup grip benefits from the same phenomenon his two-seamer does due to his natural supination.
With all of the optimization that’s used in pitch design, Gray is an example of inventing oneself based on what’s comfortable for his body. Something as simple as his inclination toward throwing with supination has a significant impact on who he is as a pitcher.
