With the year winding to a close, Baseball Prospectus is revisiting some of our favorite articles of the year. This was originally published on April 16, 2015.

Walter Johnson never threw a changeup. Babe Ruth never threw a changeup. Half of the best pitchers of the 1910s (as measured by Baseball-Reference's model for WAR) never threw a changeup. But in the century since, quality changeups and successful starters have become (with a few exceptions) nearly inseparable; 83 percent of qualifying starters last year threw a changeup or a splitter with some regularity. It's a pitch that throws power hitters off balance, that is easy to keep below the knees, and that neutralizes platoon advantages. It's been the go-to pitch for a number of great pitchers, from Trevor Hoffman to Jamie Moyer to James Shields. But while a pitcher doesn't need Tom Glavine's circle change to have a career, he most likely needs at least a quality change-of-pace to have a career in a starting rotation. It's the pitch the distinguishes most future starters from most future relievers.

“To me, it’s become the most important pitch in baseball,” an NL Central scout said. “There was once a time when you could get away with just having two pitches as a starter. Now, unless those pitches are 70 [on the 20-80 scouting scale], you are very likely headed to the bullpen if that’s all you have in your arsenal. The very best pitchers in baseball right now all have three or more pitches, and a very large portion of those will show at least a competent changeup.”

Here’s a look at what scouts look for when they’re scouting the changeup, and why it’s become such an important pitch over the past thirty seasons.

Arm speed, Arm Speed, Arm Speed
As you likely know, the changeup’s aim is to create deception; its ultimate goal being to look like a fastball for as long as possible to fool the hitter and create a swing and miss or weak contact.

How does a pitcher create that deception? Arm speed. Obviously, the pitcher can't slow down his arm and keep that deception, so he relies on the grip to do the work for him. There is typically (but not always) an ever-so-slight slowing in the arm's downward path, but if it slows too much the deception is lost. Without deception, and without the huge movement of a breaking pitch, a poorly disguised changeup becomes extremely hittable.

Here’s a great look at the negligible difference between Felix’s arm speed on his fastball and change (GIF overlay by Nick Wheatley-Schaller):

“It’s easily the most important part of the pitch,” the scout said. “The best changeups in the world, the ones thrown by Pedro [Martinez] and Felix [Hernandez] are ones that you have zero idea it’s an off-speed pitch until the pitch begins to bottom out or you see the hitter flail away.

“Too often though, you see guys whose arm slows way down; I think it’s because they think it’s just the difference in velocity that fools the hitter, and that’s just not the case. Even an average hitter can pick up on a difference in arm speed, and if a hitter picks up on a pitch that isn’t offering depth or bite that is only going 75 to 80 miles an hour? That pitch is getting hit hard a very large portion of the time. The arm speed has to be there.”

Clayton Kershaw is the best pitcher in baseball, but it’s not because of his changeup:

How I Scout Arm Speed
It sounds tricky, but it’s really quite simple. If I see the arm—whether it’s on its upward or downward path—slow down at any point, it’s something I assume a major-league hitter can pick up on as well, and the pitch grade drops for me. Think of it like a telegraphed pass from a point guard or quarterback, but instead of giving away where the ball is going by staring down a receiver, the telegraphing comes by slowing the arm path, which indicates to the respective hitter that something off-speed is coming, and essentially eliminates the deception.

Movement Helps, Too
While a change will never have the sexy movement of a plus curve or slider, it certainly isn’t meant to be a straight pitch—nothing should be a straight pitch—and its break—or lack thereof—plays a part in the grading of the pitch.

“Even if your arm speed is perfect, the pitch has to do something,” the scout said. “Personally, I always like to see a little fade to the pitch; something that moves away from the left or right-handed hitter as they’re not only off-balance, but it’s much harder to drive something going away from you. And even if they make solid contact, it’s probably being dumped the opposite way for a single. There’s nothing wrong with a power change or split change, and those probably offer the best chance of missing bats. That’s just a personal feel I get, and it’s different for every talent evaluator.”

How I Scout Movement
This one is actually a bit trickier than you might anticipate, as it’s not just as simple as asking if the pitch moves or not. Many changes appear to have downward movement, but in reality it’s just a case of the pitch nearing the end of its run and ending up below the knees. Fade is obvious though; if a left-hander throws a change and the ball breaks away from a right-handed hitter, the fade is there, and it’s just vice-versa for right-handers.

For the split-change, I typically take a look at just how hard the downward movement is and when the movement appears to takes place. If the pitch appears to start its movement near the middle of the plate, it’s plus movement. If it is past the plate, unless it makes a steep, abrupt drop, I attribute it more to the lack of velocity than anything the pitcher is actually adding.

Here we see a change with fade that causes a swing and miss:

And now, a change that does nothing and gets crushed:

The “Feel”
If you’ve ever read a scouting report on a pitcher, there’s about an 87.5 percent chance that you’ve seen the term “feel for pitching” in said report. What that encompasses exactly differs from scout-to-scout, but a substantial amount of the time, they’re including a pitcher’s comfort level with his change.

“I cannot tell you how many times I have gone to see young pitchers—at any level—throw two or three pitches that I’d grade above-average or even plus, and then they abandon the pitch for the rest of the outing,” the scout said. “I can’t guarantee it, but it’s almost always because they’re not comfortable with the pitch, and if you’re not comfortable with it and don’t trust it, it’s useless.

“Every once in a while though, you get a guy who not only has trust in it when he’s ahead in the count, but has enough confidence to throw the pitch 0-0, or even when he’s fallen behind. Those guys, the ones who know it’s a plus pitch and know that if they execute the pitch correctly have the upper-hand for the rest of the at-bat, those are the ones who go on to have long, successful careers. It’s not terribly common, but it seems like it’s becoming more and more common, and I think it’s one of the most significant reasons why we’re seeing pitchers having so much success right now.”

Not only is this the pitch of the at-bat, inning and game; it’s Felix’s first pitch of the season. Yes, The King has great feel for the changeup (GIF courtesy of Nick Wheatley-Schaller).

How I Scout Feel
As the scout said, I want to see if he can throw it for strikes and early in the count, but I’m also looking to see where he’ll throw the pitch and how well he commands the offering. If he can throw it for strikes but is missing his target, that’s a lot less impressive for me. If I see a pitcher—particularly a young one—who not only throws it for strikes but hits his spots? I know that he has feel for the pitch.

One thing that can make scouting feel a little tricky is that pitchers—again, particularly younger ones—often aren’t making the in-game decisions for what pitches they’ll throw. If at all possible, I like to speak with the coaches about what they think are the pitchers strengths and weaknesses. If they mention the change as one of his best pitches and he’s not throwing it early in the count, it could be a sequencing issue or the pitcher doesn’t trust himself to throw in the count. If the coach says it’s not a strong pitch but I get above-average or plus grades on it, I could come to the conclusion that the coach doesn’t know what he’s talking about. It happens more often than I’d like.

Also, it’s important to take the level the pitcher is throwing at into account when scouting a pitcher’s feel for the pitch. A prep is obviously going to have less feel for the offering than a big-leaguer, though I will say that if I see a high school hurler locating the change, that’s a big jump up for me. There’s no set guidelines between the levels, but it’s something you have to keep in mind.

How I Scout Velocity
The average changeup for major-league starters who qualified for the ERA title last season threw their changeups about 7 mph slower than their fastball. Typically, I like to see a velocity difference higher than that; ideally in double digits but with at least a 10 percent difference from their heater to the change—particularly with younger prospects. Guys like Cole Hamels and Hernandez who have pinpoint command of their pitch with loads of movement—and can thrive with somewhat lower differentials—are outliers to me. The change exists to fool the hitter (you’ve likely heard the term “pull the string”) and the velocity difference can at least keep hitters off-balance while a young hurler develops command and movement with the pitch. Is it a necessity? Perhaps not, and Harry Pavlidis found that changeups with smaller differentials get more groundballs (if fewer whiffs), but I see big benefits in the velocity difference.

The Splitter/Forkball
The splitter/forkball/split-fingered fastball/whatever you want to call it is very similar to the change in that you’re looking for the same things you’d be looking for in a change—arm-speed, movement, feel—but with the added caveat that depth is much more important for these offerings, as scouts want to see these pitches “fall off the table.” When they’re effective, they’re a lot of fun to watch, but because they’re so hard to control, you typically don’t see a lot of starters throwing them anymore. That’s not necessarily a bad thing.

It’s not as easy as scouting a fastball or speed on the bases, but I personally believe scouting the change is one of the easier pitches to scout if you know what you’re looking for. The beauty is in its simplicity, and while it’s not easy to break down unless you’re sitting in front of the pitcher, it’s a beautiful thing to watch when you are aware of what a good one looks like.

The Neyer/James Guide to Pitchers provided valuable information about old-time repertoires for this article.

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