Tonight, Luis Severino will take the mound against the Boston Red Sox to start his long-awaited MLB career. A native of the Dominican Republic, Severino was signed in 2012 to a $225,000 signing bonus. As he added mass through the Yankees' strength and conditioning program, his fastball spiked from the high 80's/low 90's to the mid-to-upper 90's. But is he really ready for the show? By a variety of measures, it sure looks like it.
If you're a regular reader, you might notice that we will often turn to the KATOH projection system for minor league pitchers. For those who don't know, the KATOH model is a statistical model which estimates the likelihood of a minor league prospect reaching the MLB and accruing different levels of WAR by his age-28 season. According to the KATOH model, designed by Chris Mitchell for The Hardball Times, the only statistically significant metric for rookie level leagues and short season A- leagues is a pitcher's strikeout rate. At Class A and up, BB% begins to be statistically significant.
In 2013, Severino started with the Gulf Coast Yankees at the rookie league level, where he amassed a very impressive 31.4% K%. From that point until his time at Triple-A Scranton Wilkesbarre, he continued to strike out more than a batter per inning, never allowing his BB% above 7.5%. But the exciting thing about Luis Severino is the possible reason why he experienced so much success in the minors.
Looking at various scouting reports, the general consensus is that Severino's changeup has developed into a plus pitch, while his breaking pitches are still improving. While Pitch F/X data isn't available for his time in the minors, it stands to reason that he was able to blow hitters away relying mostly on his fastball, especially at the lower levels, since he was still developing the other pitches.
A real world case study that illustrates the importance of an excellent fastball is just a subway ride away with the New York Mets. According to Brooks Baseball, Jacob deGrom, Matt Harvey, and Noah Syndergaard all throw fastballs roughly 60% of the time. According to Fangraphs, the league average starter throws his four seam fastball, two seam fastball, or sinker 46.6% of the time. Because the Mets' young hurlers are able to get good velocity, life, and location on what are by far their most common pitches, they have experienced a much easier learning curve in the MLB.
If Severino was striking out batters left and right even in the lower levels of the minors, it is probably because he has a very good fastball. Even his mechanics are comparable to pitchers like deGrom or Harvey, as seen in the gif below. Notice how his right arm circles around without stopping before he releases the ball:
All three of the Mets pitchers mentioned above will essentially do the same thing. They right arms will take a pretty straightforward route from their gloves to their release points. Pitchers like Ubaldo Jimenez, Tim Lincecum, and even the Yankees very own Nathan Eovaldi will all have somewhat of a pause in their motion, where their arms are fully extended. They also have all had their struggles with command at some point. Ubaldo Jimenez is a great example of the "pause" in the delivery, as he will fully extend his arm behind his back:
Luis Severino might struggle in the big leagues for a wide variety of reasons. But if he does have a tough time in pinstripes, it won't be because his foundation is weak. Even though he is just 21 years old, look for him to paint the corners with his fastball. If Larry Rothschild can help him develop his secondary pitches as much as he has helped Eovaldi, the Yankees just might have their next front-of-the-rotation starter.
*Unless stated otherwise, data is courtesy of Fangraphs.