Aroldis Chapman’s renaissance by the numbers


Aroldis Chapman is having a renaissance season.  He was pretty good for most of the year last year, before an awful stretch in August brought his overall numbers down. Last year he finished the season with a 3.22 ERA, 2.56 FIP, and 1.6 WAR. Perfectly serviceable, however, so far this year he has a 1.46 ERA, 1.05 FIP and already 1.3 WAR. Let’s take a closer look as to why that is.

Better fastball results

In 2017, Chapman’s fastball whiff rate (percentage of pitches swung at and missed) was 27.2% according to This year so far, his fastball whiff rate is up to 35%.  That’s a huge improvement. Even when hitters make contact with his fastball, they aren’t doing much with it. Last year batters hit .190 against Chapman’s fastball and slugged .282. However, this year, it’s been even better. Batters are hitting a paltry .127 against the fastball and slugging only .206. Even though Chapman has lost about a mile per hour on the pitch this season, he is getting better results.

Better slider results

We’ve seen a stark improvement in Chapman’s slider in 2018. Consider last season, his slider was only slightly above average according to Fangraphs. The pitch was worth +0.6 runs above average. So far this year, the slider is already worth 2.2 runs above average. This is a cumulative stat, so as the season goes on that number will increase, assuming he is still getting good results with it. This is where it gets very interesting. In 2017, Chapman’s whiff % on the slider was 45%, in 2018 it’s 68.2% so far, which is otherworldly. Batters are hitting only .158 against the slider, and don’t have any extra base hits off of that pitch either.

Statcast nugget

Statcast has a hit type classification called “barrels.” I’m going to spare you the nerdy classification of this hit type, but it’s exactly what you think: pitchers don’t want to give up barreled balls. They typically are home runs, or at the very least extra base hits. Chapman has given up ZERO barreled balls this season. Hopefully that continues this season and well into October.


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