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Is Aroldis Chapman evolving?

Yankees closer Aroldis Chapman has always been known for one thing: his heater. The Cuban fireballer took the league by storm in 2010, clocking the fastest pitch ever recorded at 105.1 mph. From 2014-2017, Chapman threw 1,870 fastballs at a speed of 100 mph or greater. That was nearly six times more than Mauricio Cabrera’s 342, and represented 37.5% of all fastballs registered in triple digits in the entire MLB.

Chapman was no circus freak either. He quickly demonstrated that he could be an elite big league reliever, posting a 2.17 ERA and 15.40 K/9 in his nearly six years in Cincinnati. There was little deception or mystery in Chapman’s approach. He averaged greater than 80% fastballs over his time with the Reds, peaking at an unheard of 88.0% rate in 2012. Nobody in baseball was throwing fastballs at such a high clip, let alone having his level of success doing it.

There was a good reason for that fact. The average velocity among relievers across the MLB was just 92.4 mph in his rookie season. Even as velocity rose steadily across the league, Chapman continued to find success with his overpowering fastball. Contact rates against him were consistently lower than other pitchers in baseball. From 2010 to 2016, Contact% against him averaged 16.2% lower than the rest of the league. Everybody knew what Chapman was going to do, but nobody could really do anything about it.

That started to change last season. His Contact% jumped to 73.2%, nearly ten points over his previous career high and just 4.3% better than the league-wide rate. With it came his highest ERA and FIP since his first full season, an indication that hitters were starting to figure him out. Worry among Yankees fans peaked during his abysmal month of August. He pitched to a 9.00 ERA and his K% plummeted to just 21.1%, a huge drop from his career 41.6% rate. He couldn’t buy a swing and miss, with his fastball whiff percentage at a career-low 7.6%. Doubt about his massive contract crept into the minds of every Yankees fan.

But something has changed at the start of this year. Though the season is young, Chapman’s Contact% and K% are better than at any point in his career. His minuscule 1.29 ERA and 0.40 FIP demonstrate just how dominant he’s been through the first month. Especially since his April 11th outing against the Red Sox, Chapman has been absolutely lights out. In 8 IP since that appearance he’s allowed no runs on just three hits and three strikeouts. He struck out 16 (!) over that span. What explains this sudden resurgence for the Yankees’ closer?

One interesting trend is the steady uptick in horizontal movement on Chapman’s four seam fastball over his little hot streak. His eight innings since the Boston outing have seen a consistent improvement in horizontal movement. Especially in Houston with their camera angle, the tail on Chapman’s fastball was astonishing. 100+ mph without movement is hard enough to hit. That kind of velocity with 5 inches of horizontal movement? Unfair.

Similarly, the only two outings of the year where he’s struggled were his second outing against Toronto and his appearance against Boston. Those were his two worst days in terms of horizontal movement on his fastball. Unsurprisingly, he was much more mortal in those two outings and got hit fairly hard by the opposition. It’s still early, but it seems like Chapman may be sacrificing some velocity for movement to great effect.

Another early trend has been Chapman’s increased slider usage. He used it more in April than any other month in a Yankees uniform, and seemed to be increasing his usage even further in his Houston appearances. The logic here is simple: it’s harder to hit when you don’t know what’s coming. Hitters have been sitting fastball on Chapman his whole career, and he’s rarely been burned by it. Last year, that no longer was true. Adding a slider to his arsenal puts doubt in the hitters mind, making his fastball seem even faster and generating whiffs when he spins a good one.

On top of all this, there’s one more interesting change with his slider: the speed. While the movement on the pitch has stayed mostly the same, he’s slowed the pitch down to about 86 mph rather than the 88+ mph he used to throw it at. This has added to the velocity difference between his fastball and his slider, making both pitches stronger.

It’s too early to say definitively that Chapman is changing his game. This could easily be an example of small sample size noise driven by either random fluctuations or early season adjustments. But it seems clear that when Chapman has his fastball dancing, hitters can’t even dream of touching it. When he adds in a slider, even just to show it to the hitter? He’s downright unhittable. Regardless, let’s hope this dominant Chapman is here to stay.

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