Curveballs can move laterally, vertically, or both. They can feature a sharp, late bite, or they can rainbow from a hitter's ear to the outside corner of the plate at his ankles.
While it's easy to look at a curveball with a lot of movement and fall in love, the two most important factors when rating a curveball are neither velocity nor movement (though obviously, both of those are important). They are command and deception. A good major league hitter can lay off most curveballs in the dirt and cream even a good curveball if he can tell one is coming from the pitcher's delivery.
When a pitcher is getting outs in the lower levels with his curveball, he is often either fanning hitters who can't lay off a good curveball no matter where it is pitched or throwing strikes with a mediocre curveball to neophyte hitters that can only hit perfectly straight pitches. When scouts say that they aren't sure how a pitcher's secondary stuff will play at higher levels, they usually mean that there isn't enough bite to it, but lack of command and lack of deception will cause a pitcher to hit a wall in Double-A as well.
The Arizona Diamondbacks have a better stock of sliders than curveballs in their organization overall, though some of the organization's best sliders have sometimes been described as power curveballs, especially those of Esmerling Vasquez, Scott Maine, and Wade Miley. Many inexperienced pitchers will throw a slurve, which is something in between a slider and a curveball, and generally not a great way to get advanced hitters out.
Here are the FutureBacks curveball prospects rankings, factoring in both how good the curveball is now and where it projects to be at its peak.
1. LHP Daniel Schlereth
Schlereth uses the epitome of a power curveball that usually hits 80-82 miles per hour. Scouts, coaches, and hitters are often left without adequate words to describe this plus-plus offering. Pioneer and Midwest League hitters had no chance against it, as they combined to bat just .146 against him total. Its late-breaking action will continue to befuddle hitters at higher levels. The one problem here is that Schlereth's violent mechanics not only make him an injury risk, but also make the command of his pitches erratic at times. That includes the curveball; advanced hitters will be able to lay off the ones in the dirt.
"I just feel a lot better throwing the curveball. I feel like I have a little more command of it right now at this point in my career," says Schlereth when asked about his curveball and changeup.
"He has a major league curveball," insists Mark Haley, Schlereth's manager at South Bend.
2. RHP Billy Buckner
The curveball has been Buckner's claim-to-fame since his days in the Royals organization, and he has definitely improved his command of this sharp-breaking pitch over the past few years. Buckner isn't afraid to use the pitch against left-handed batters, who often have trouble zeroing in on it just as righties do. The pitch sits at 79-80 MPH, which isn't a true power curve, but also certainly not a slow one. It's about 11 MPH slower than his fastball, which can deceive batters effectively given the low trajectory and identical arm slot he has for the pitch.
"Buckner's curveball ranks pretty high up in our system," confirms director of player development A.J. Hinch.
3. RHP Jarrod Parker
Right now, Jarrod Parker's slider ranks well above his curveball, but scouts really like the potential of Parker's curve as a strikeout pitch. The curveball has a nice spin on it, but it isn't exactly falling off the table yet. His inability to command the pitch with any regularity is more of a concern right now than anything movement-wise. It has been clocked anywhere between 77 and 80 MPH, and it reportedly improved a great deal in this fall's Instructional League.
"He made some adjustments," says Instructs field coordinator Jack Howell. "He continued to work on his secondary and third pitch, and he jumped right on it and had a great Instructional League."
4. RHP Matt Torra
Diamondbacks fans should be very happy that no team was willing to take a chance on Matt Torra in Thursday's Rule 5 Draft. The 31st-overall pick in the 2005 draft, Torra has an excellent combination of power, balanced repertoire, size, command, and pitching acumen. The one knock on him is his health, as he needed to undergo labrum surgery shortly after being drafted. Before the surgery, Torra had a 12-to-6 power curve that sometimes hit 83 MPH. It's a notch slower and more of an 11-to-5 offering now, but still got both Double-A and Triple-A batters out consistently this year.
"My curveball's the same thing with my velocity; now that my shoulder's a lot stronger, I feel it's going to really come back to where it was before," says Torra.
5. RHP Cesar Valdez
Here's a guy with a big, looping curve. Scouts didn't think it would fool advanced hitters, but in 2009, Valdez proved them wrong. The break may be big and slow, but it's far from a rolling, predictable break. He isn't shy about using it against left-handed batters, and peppers it in with two straighter offspeed pitches to keep all hitters guessing. As effective as Valdez had been without a plus-fastball, you know his secondary stuff has to be good. His changeup is still his best pitch, but his curve stacks up well in this slider-heavy organization.
Honorable Mention: Aptos high school draft pick Kevin Eichhorn reportedly wields an excellent curveball, but we need to see him use it against advanced hitters before we can rank it here.
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