Aroldis Chapman doesn’t throw all the hardest pitches in baseball, but he does throw most of them. Last year, PITCHf/x captured 41 pitches of at least 102 miles per hour. Of those, Chapman was responsible for 27. He throws the kinds of rockets that make even rival spectators gasp, and indeed, the heat has long been his calling card. It’s one of the most exceptional abilities in the game. Chapman throws a lot harder than just about anyone. But what if he didn’t?
In a sense, this is a hypothetical. In a sense, this can be investigated. What if we chopped a few miles per hour off Chapman’s average fastball? We can’t know for sure what that pitcher would actually be like, but we can make something of an educated guess, based on Chapman’s history. So let’s try it, just to see. Big thanks to Brooks Baseball for making this fairly easy.
We’re interested in Chapman when he throws in the 94 mph to 96 mph range, or so. But we can’t just isolate those slower fastballs. Things aren’t that simple. What if one of those slower fastballs came in a game in which Chapman was averaging nearly 100 mph? Then it would function almost as a pseudo-changeup, a minor change of pace. No, it’s better to focus on Chapman’s lowest game averages. I’ll try to keep the methodology to a short paragraph.
From Brooks Baseball, I exported Chapman’s single-game fastball velocity averages. In all, his fastball averaged 98.1 mph, with a standard deviation just less than 1.7. Subtracting the standard deviation from the average yielded just under 96.5 mph. I decided to isolate Chapman’s games in which his fastball averaged something below that mark. I was left with a sample of 36 appearances. Over these 36 appearances, Chapman’s fastball averaged 95.6 mph. So, rather than throwing like Aroldis Chapman, he threw like a really talented baseball player. Last season, John Axford‘s fastball averaged about 95.3 mph. Luke Hochevar‘s fastball averaged about 95.4 mph. This is a good fastball — a fast fastball — but a diminished fastball from Chapman’s established norm.
So what do the other numbers say? How did Chapman perform over his 36 slowest relief appearances? This is to be the basis of our educated guess. And, you know, things could be better. Over these appearances, Chapman threw just 59% strikes. He walked 19% of 151 batters. Over all his other appearances, he threw 64% strikes, and he walked 11% of more than 600 batters. The slower Chapman has been, the wilder Chapman has been.
But, my goodness, that isn’t everything. Slower Chapman also struck out 36% of the batters he faced. He allowed a contact rate of 67%. He allowed three home runs, for a rate which isn’t meaningfully different from his ordinary rate. Last year, 125 relievers threw at least 50 innings. Five managed strikeout rates of at least 36%, including Chapman. Slower Chapman has a higher strikeout rate than Trevor Rosenthal.
And there’s a very important consideration. Aroldis Chapman averages 98 mph with his fastball. We’re looking at a sample of games over which he’s averaged less than 96 mph. So this is selecting for games during which Chapman wasn’t quite right. Put another way: What would Chapman be if his 100% was throwing 95 mph to 96 mph? What we’re looking at are games in which he was throwing 95-96, but he wasn’t 100%. He’s dealt with shoulder fatigue before, and this can lead to performance issues that sometimes manifest as subpar control. That’s a likely explanation for the high observed walk rate. Slower Chapman is also not-normal Chapman, which means the numbers we see might reasonably represent the bare minimum, or so.
So let me summarize real quick. The question: What if Aroldis Chapman lost a few miles per hour? When he’s pitched below his norm, he’s walked a lot of batters, and he’s struck out a ton of batters. The walk rate might be explained by the fact that these are games in which Chapman wasn’t quite OK. And when he wasn’t quite OK, he still posted what would be one of the highest strikeout rates in baseball. So if healthy Chapman averaged about 95.6 mph, he might strike out even more batters. After all, it’s easier to do better when your arm feels better.
Here are examples of Chapman throwing in the mid-90s, for the hell of it:
When he’s thrown softer, Chapman still hasn’t thrown soft. A fastball between 95 mph and 96 mph is still a really good fastball, an above-average fastball even among the pool of relievers. I don’t know how to test what Chapman might be around 92 mph to 93 mph. When he’s thrown softer, Chapman hasn’t been literally unhittable, but he’s been about as close as any other pitcher. So there’s reason to believe that even if Chapman lost a few miles overnight, as long as he were healthy, he’d still function as a strikeout machine.
Mostly, I did this out of my own curiosity. But the other night I was wondering how long Chapman might be able to keep throwing as hard as he does. Velocity tends to diminish, and Chapman’s pressing against the upper extreme. Velocity-wise, Aroldis Chapman can’t be this version of himself forever. Performance-wise, though, it looks like he could still get the job done, even as a more ordinary hard thrower. Eventually, Chapman might be reduced to throwing 95 mph. And should that day come, opposing batters probably still will really hate him.
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