Aroldis Chapman could be even more effective by being less predictable with his fastball

By any objective measure, Aroldis Chapman is one of the best relievers in baseball and most dominant single-inning forces in baseball history. Chapman has struck out 42.6% of the batters he’s faced in the big leagues, including 44.2% over the last five seasons, the highest rate in history by nearly two percentage points. Craig Kimbrel (40.7%) and Kenley Jansen (39.8%) are the only pitchers within nine percentage points of Chapman.

As good as he is, Chapman is not without his flaws as a pitcher. No player is perfect, after all. Chapman does walk a few too many hitters (career 11.6 BB%), and yeah, he’s made it known he prefers to work the ninth inning and only the ninth inning. Chapman can also be a bit predictable on the mound, especially when he falls behind in the count. (And since he walks so many batters, he’s behind in the count more often than the average pitcher.)

I first noticed this during Chapman’s short stint with the Yankees last year, but he was here and gone so quick — Chapman was on the active roster only 76 days between his suspension and the trade — that I never got around to looking into it. Since he’s back for at least three and possibly as many as five years, it’s time for a deeper dive. Here is Chapman’s pitch selection over the last three years:

There are two obvious caveats here. One, every pitcher throws more fastballs when they’re behind in the count. Last season pitchers threw a fastball 64.4% of the time when they were behind in the count. It was 56.2% when the count was even and 48.4% when ahead in the count. And two, not every pitcher has Chapman’s fastball. No other pitcher does. He’s one of a kind. Life is good when you throw 100 mph on the regular.

Chapman, when he falls behind in the count and needs to even things back up, will lean on his high-octane fastball and understandably so. It’s the most dominant fastball in baseball history. There’s no point in keeping it in your back pocket. Aroldis is leaning on that pitch when behind in the count more and more with each passing year too. It was 80.5% fastballs three years ago, 84.6% two years ago, and 89.1% last year.

Again, Chapman’s fastball is historically great, so throwing more of them seems like a good idea. Look at his numbers when he’s been behind in the count the last three years though:

Count Even: .199/.216/.269 (40 OPS+)
Pitcher Ahead: .068/.071/.083 (-40 OPS+)
Batter Ahead: .263/.526/.391/ (93 OPS+)

When Chapman gets ahead in the count, forget it. Game over. Opponents have a .154 OPS (OPS!) against him when he’s gotten ahead in the count since 2014. Crazy. When the count is even, Chapman is still dominant. The hitter might as well be down 0-2.

But, when Chapman falls behind in the count, he’s damn near average. Keep in mind a 93 OPS+ in those situations still isn’t great for the hitter, but relative to Chapman’s standards, it feels like a miracle. Hitting .263 against a guy throwing that hard is impressive, and I can’t help but wonder whether Chapman’s predictability with the fastball plays into that. Sure, he throws extremely hard, but if hitters know it’s coming, their life gets a little easier.

The best way to look at this is by isolating Chapman’s fastball. Here’s how hitters have performed against his fastball in the various count states over the last three years:

I literally lol’d at the .005 ISO against Chapman’s fastball when he’s ahead in the count. Aroldis has allowed one extra-base hit against the heater when he had the count advantage over the last three seasons. One. It was a Garrett Jones double on an 0-2 fastball in August 2014. (I went back through MLB.tv to see if there was any defensive funny business, but no, it was a booming double off the top of the wall on a mistake fastball down the middle. So it goes.)

Anyway, hitters have had more success against Chapman’s fastball when he’s behind in the count. A lot more success. They’ve hit for more average and power, and swung and missed a heck of a lot less. (A 13.9% whiff rate on a fastball is still insanely good, I should note.) I thought maybe this would explain the foul balls too — Aroldis does seem to give up a lot of fouls, doesn’t he? — but apparently not. Either way, Chapman’s fastball is not nearly as effective when he’s behind in the count, yet that’s the pitch he’s throwing nine times out of ten in those spots.

Based on this, it’s fair to wonder whether Chapman would benefit from using his slider and changeup a bit more often when behind in the count. Not necessarily when he’s down 3-0 or anything like that, but in 1-0, 2-0, or 2-1 counts, when a ball doesn’t put a man on base? Why not? The goal is to put something else in the back of the hitter’s mind and change the scouting report. That’s why Chapman’s fastball is so good when he’s ahead in the count. He throws the most sliders and changeups in those spots and the fastball plays up. Right now, hitters can sit fastball when he’s behind.

This is nitpicking to the nth degree, of course. Chapman is historically great even while throwing all those fastballs when behind in the count, so he doesn’t have to change anything to remain effective. This is more a look at a way Chapman can be even better, which is pretty crazy to think about. Mixing in a handful of sliders and changeups when behind in the count, just a few to stop hitters from sitting heater, could make a pretty significant difference.