Is Luis Severino’s fastball better than ever?

Luis Severino’s fastball has never been under more scrutiny than it was in his past two starts. With the starter’s return from shoulder and lat injuries came plenty of questions about his ability to dial up the high-90’s four-seam fastball that helped make him so successful the past two seasons. In some ways, Severino has exceeded expectations, and he’s dominated in nine innings of work since his return from the IL on September 17.

Last season, Severino averaged 97.6 mph on his fastball, according to Statcast. While the Yankees would obviously love to see Severino reach that same velocity this season, that kind of velocity is not necessarily needed for the 25-year-old to succeed as a front-line starter. For comparison, Gerrit Cole leads all starting pitchers with an average fastball velocity of 97.1 mph this season. Since Severino’s return from the IL, his average fastball velocity is 96.6 mph, and he’s reached as high as 98.8 mph on multiple occasions. His fastball might not be all the way back to the same velocity as last season, but he’s shown he still possesses one of the league’s highest-velocity heaters.

As electric as Severino’s fastball was last season, opponents had a fair amount of success against it. Opponents posted an xBA of .282 and an xSLG of .483 against Severino’s fastball last season per Statcast, making his fastball the least effective of his three pitches. His struggles with pitch tipping are well documented, so that could be one reason he struggled to fool batters with such high velocity.

Whether it was pitch tipping, a lack of movement, or poor location, Severino posted a whiff rate of 20.2% on his fastball in 2018. For comparison, J.A. Happ, with an average fastball velocity of 92.3, posted a 24.4% whiff rate. However, the whiff rate on the 82 four-seam fastballs Severino has thrown this season is all the way up to 42.9%, more than double his percentage from last season and higher than both Justin Verlander (31.3%) and Gerrit Cole (37.3%). Opponents are a combined 2-for-13 with seven strikeouts against Severino’s fastball, offering great encouragement for the Yankees coaching staff as playoff time approaches. But how is Severino getting so many swings and misses on a fastball with slightly diminished velocity?

The easy answer is that Severino’s faced depleted Angels and Blue Jays lineups across small samples in the 2019 season. Still, doubling your whiff rate is likely more than the result of facing a couple sub-par lineups. Perhaps Severino is hiding the ball more effectively in his delivery, but his fastball is also generating more movement than it did last season. In 2018, Severino’s four-seam fastball averaged 6.4 inches of horizontal break and 12.6 inches of vertical drop. In his first nine innings of 2019 he’s averaging 8.2 inches of horizontal movement and 13.2 inches of drop, according to Statcast.

Whether it’s by design or not, Severino has also created a larger gap in velocity between his fastball and his breaking ball. Severino’s slider velocity averaged 88.1 mph last season, and is all the way down to 85.0 mph (with increased vertical drop) through his first two outings. Combine that with an increase in changeup usage, and it’s possible Severino will have more success keeping batters guessing this season, making it harder to time his elite fastball.

It’s a very small sample size to analyze, especially for a player who’s just returning to the mound in September, but it appears the Yankees’ patience with Severino’s recovery is paying dividends. If Severino can continue to generate swings and misses with his fastball at the rate he has thus far, nobody’s going to want to face him twice in a playoff series.