After averaging 98.3 mph on his fastball in Sunday night’s marathon of a game, the same Luis Severino that went down with a tricep strain a year ago Friday, causing many of us without retrain to give up on a 22 year old arm, currently sits atop the velocity leaderboards on his fourseam fastball (starting pitchers, min. 200 pitches).

Bronx’s budding star sits ahead of titans on the velocity front, eclipsing names like Stephen Strasburg, Chris Sale, and Jacob deGrom. Severino’s average fastball velocity of 97.7 mph this season is one half mile per hour ahead of Gerrit Cole and more than a full mile per hour ahead of James Paxton. If the city of New York was looking into alternative sources of energy to power the city, they might want to tap into this 23-year-old’s electric heater.

Fellow BP Bronx writer Austin Yamada astutely pointed out the widening of Severino’s ‘velocity gap’ between his fastball and his primary offspeed pitch, the devastating slider we’ve come to love (Yamada also made a great comparison to Rays’ ace Chris Archer, which I cannot steal from him, but sure as heck want to). I’m here to also point out the other velocity gap that widened since last season and has led Severino to the promised land of left handed hitter domination.

An issue with simply looking at percentage pitch usage is that we often glaze over changes in how a pitcher is throwing a certain type of hitter. We may look at the aggregate usage of a certain pitch versus all hitters and see a decrease, but remain blind to an increase when splitting up the usage by a simple factor like left handed versus right handed bats.

This theory of mine applies conveniently to Severino. On the left below we have Severino’s change in changeup usage to all batters between 2016 to 2017. Our graph on the right shows his changeup usage just to left handed bats between 2016 to 2017.

Sure it’s a small fraction of an increase, but that uptick is important, especially if you look at how virtually unhittable the pitch has been to left handed bats…

Lefties possessed a .263/.331/.416 off Severino in his 71 innings of work, which has bottomed out to a dismal .178/.213/.352 so far in 2017. Trusting his changeup more to lefties has allowed him to escape the tag of a pitcher with heavy lefty/righty splits, forcing managers to rethink throwing a lefty heavy lineup at the Yankees’ young star and praying for a few misplaced offspeed pitches.

Severino has tinkered with his approach to both sides of the plate, and it’s working. More changeups and fastballs to lefties, more sliders and virtually no changeups to righties.

Back in Januray of last year, the great Jeff Long called back to a Baseball Prospectus column by Harry Pavildis that broke down what makes a good changeup. You can read the article here, but I’m going to cherry pick the high level points Long summarizes in his column. There are four factors in a pitcher’s repertoire that help to make a changeup effective.

Faster fastballs result in more whiffs on the pitcher’s changeup. Severino’s velocity is up (96.7mph to 97.7mph from 2016), but he isn’t seeing a noticeable increase in either his swinging strike rate or strikeouts as a whole with his changeup (whiff % is down, 7.3% to 3.6% from 2016 to 2017). “Velocity gap,” or the difference between a pitcher’s fastball and changeup velocity also results in more whiffs. This gap for Severino has increased a noticeable amount, just like his fastball-slider velocity gap. In 2016 this difference was about 7mph. This season it’s up nearly 3mph, to just under 10mph of difference between his fastball and changeup. Oddly enough, even though Severino is 2-for-2 on these changeup traits, we’re still sitting on a decrease in whiffs with the pitch. Pitchers with higher changeup whiff rates, throw their changeups more. We have to disqualify Severino on this one because as I’ve already pointed out twice, Severino’s changeup whiff rate has actually decreased. We’ll get to the bottom of this, I promise you. The vertical drop of changeups relative to fastballs increases both the whiff and groundball rate. This is a factor we haven’t touched on with our young stud, but a good one to consider. Severino’s changeup vertical movement increased from 5.6″ in 2016 to 6.9″ this season (more “sink”). With his fastball vertical movement steady from 2016 to 2017, the extra sink on his changeup relative to his fastball can add more whiffs and grounders to the pitch’s results. Ah! There is what we have been searching for. More grounders! Severino’s changeup has in fact seen a nice increase in grounders per ball put in play. Last season it was at 46.2% while this season it has edged up nicely to 54.6%.

One more thing to consider in order to further understand why we’re still not seeing more whiffs with the changeup is to realize the velocity at which Severino is throwing his changeup.

In the article I linked to above from Jeff Long, he mentions the wonky relationship between whiffs and grounders with changeups, noting that changeups with higher velocities actually result in more groundballs realtive to whiffs. Our big takeaway here is that even with the nice drop in velocity on Severino’s changeup, widening the velocity gap between the pitch and his fastball, the pitch itself is still a high velocity offering compared to the rest of the league. At 87.9mph, he has the 15th hardest changeup in the league among starters who have thrown the pitch 50+ times.

Nestled right in the 83rd percentile for changeup velocity, the overlooked pitch of Severino’s arsenal deserves some respect as it has kept him honest against left handed bats. With the concept in hand that higher velocity changeups lead to more groundballs, I’m not concerned one bit that Severino isn’t getting enough swinging strikes to maintain his success against left handed bats. Combine this with the increased velocity gaps between both his fastball-slider (previously discussed by Austin Yamada), and his fastball-changeup discussed here, and it’s no surprise we’re looking at a pitcher with a pristine 1.64 DRA.