Curveball vs. Slider - Here Are Difference

We are reader supported. When you purchase through links on our site, we may earn an affiliate commission. Also, as an Amazon affiliate, we earn from qualifying purchases.

New fans of baseball will hear certain terms and maybe think they know what it means. This is especially true for certain types of pitches, such as a curveball vs. slider, or even the knuckleball. What does it mean that a ball curves, or “slides.” Or, what does a ball do when it “knuckles”?

In baseball, a curveball is thrown at a slower speed than a slider; and a curveball breaks downward, compared with its cousin pitch that “slides” laterally, or side to side. They are distinctly different offerings to hitters.

Key differences: the curveball delivery features a downward yank on the ball at release, pushing the ball to drop from the apex of its flight to the catcher. The slider has a hard lateral spin created by special grip and finger pressure on the ball.

Then there is the knuckleball, which really should be called the fingernail ball, but we’ll get to that later.

Regarding the curveball vs. slider discussion, there is much to be said about Major League Baseball successes with each, and also about their drawbacks. Namely among the latter is the stress both place on a pitcher’s elbow.

But not all pitcher’s arms are the same, and some hurlers toss these breaking pitches for many years. Let’s take a look at the details and tendencies of these long-favored benders.

What is a Curveball or a Slider?

The curveball is the grandfather of non-fastball pitches, as its origins can be traced back to the 1860s, while the slider did not surface until around the 1920s. Since then, a great variety of hybrids have come along, like the slurve, and cut fastball.

All involve a pitch that does not come at the batter in a straight line. Hence as a group they are called “breaking” balls, or sometimes “off-speed” pitches. This basically means not the same speed as the fastball, which is thrown at (or near) a pitcher’s top exertion level.

Fastballs can succeed against hitters through sheer velocity, locations (e.g. inside or outside, up or down depending on a hitter’s known strengths), and possibly some natural movement. Fastballs, too, can move while in flight, usually because of how a particular pitcher grips or throws it (like Hall of Famer Mariano Rivera). It all comes down to aerodynamics, which we’ll discuss below.

About those Seams

Baseballs have seams, the spot where two cuts of rawhide are sewn together, forming a unique shape on the ball, as if two horseshoes were stuck together at their open ends. Basically, two rounding oblongs connected by a thinner center piece.

Seams are the key to making a baseball pitch move. First, the seams dictate how a pitcher will grip the ball for a certain pitch. Fastballs are usually gripped with the index and middle finger either perpendicular to a seam (4-seam fastball), or parallel with/on top of seams (2-finger fastball). When released, the ball has a backward spin.

Curves and sliders are gripped along a seam, but off to a side, or not centered on the ball. The curve especially requires a strong snap of the wrist upon release to get the ball spinning enough to grip the air and move straight or diagonally downward. For the curveball, the pitcher snaps the ball so it spins forward (and not backward like with the fastball).

A slider is similar, but not quite. The curve grip depends much on the middle finger, while the slider is guided more by the index finger. The slider is thrown with more of the same arm action as a fastball, and tossed about as hard, letting the grip and a slight twist of the wrist at the very end cause the late ball movement side to side.

Types of Curves and Sliders

Even among the pitches there are variants:

12-6 curveball. When thrown completely overhand, with the forearm coming vertically up then down, the ball breaks straight down — as if from the 12 to the 6 on a clock face.
Sweeping curve. This variant is thrown with an angled arm slot, say at 75%, or between straight overhand and straight sidearm. This makes the break down along with toward the off-hand (gloved hand), for a long, looping diagonal type of toss.
Hard slider. Thrown only 5 to 7 mph slower than the fastball.
Slider. Comes 7 to 9 mph slower than fastballs.

Breaking Pitches and Aerodynamics

Baseballs have weight, and when thrown or hit they spin in various ways and are subject to the laws of aerodynamics. What influences this greatly are those seams noted above — because they are raised slightly above the surface of all the rawhide and as such get affected by the air as the ball flies.

Air molecules grip objects on a baseball, like the seams, and can push it. Not just the seams, but any imperfection on the ball, like a glob of saliva, or a deep scratch or cut. (The former is an example of a spitball, and the latter, well, are just illegal pitches; it’s why umpires often inspect pitched balls that bounce in the dirt, to prevent the pitcher from using a blemished ball as an advantage).

Depending on how a baseball is thrown, the seams could “bunch up” one one side, creating more weight there, and/or gripping the air more. It’s like leaning slowly to one side when you hold a heavy weight only in one hand.

Batters sometimes refer to a “dot” they see on the ball with sliders — because the seams are aligned in a way that, when spun hard sideways, creates the illusion of a red dot (because the seams are red) on the otherwise white object coming at them.

How hard a ball is thrown impacts the ball movement also. Curveballs are really the work of the pitcher and his wrist-snap action at the end, creating a tremendous spin totally different than that of a regular fastball. Quite often, pitchers find their curves break more if they toss them slowly. Some can appear like high looping pitches that drop to the catcher, yet they are still thrown plenty hard.

Sliders are thrown harder and don’t necessarily depend on the angular spin, but more on the grip and fastball-like arm slot.

Deception with Off-Speed Baseball Pitches

Aside from ball movement, curveballs and sliders depend on disrupting the timing of the batter, who usually loads up pre-pitch to look first for a fastball, then hopes to adjust quickly to other types of pitches. The more a pitcher can use the same arm action as a fastball, while at the same time throwing a pitch that arrives slower, the better. The average curveball speed in the MLB is 77 mph — compared with the 90+ mph of fastballs.

Timing is such an integral part of hitting that pitchers go to great lengths to hide which pitch is coming. Their gloves are usually the type with closed pocket webbing, so no one can see their fingers on the ball inside the mitt. They also must be aware of little things like a finger inside the glove popping up only when he throws curveballs; or a slight jerk of the head on fastballs. These are called tipping pitches — a little help for the batter to know what to expect.

Just that little knowledge — that a curve is coming rather than a fastball — tells the hitter to stay back and wait to swing a tad later, because the ball will not speedily zip over the plate. Messing with hitters’ timing is a huge part of pitching success.

As is mixing up pitches, and locations. But that’s an article for another day. All that said, which pitch is harder to hit, the curve or the slider?

Individual Pitcher Skill, or Batter Tendencies

Which pitch is better totally depends on the skill of the pitcher chucking it. Some famed pitchers like Sparky Lyle, Ron Guidry, and Steve Carlton had fierce sliders they used to perfection for stellar seasons and long careers. Others like Clayton Kershaw had stupendous curveballs that they rode for long-term success.

It also depends on the hitter. Some batters like Tony Gwynn have awesome eyesight and ability to determine what the ball will do right out of the pitcher’s hand. This helps with timing and stride, adjusted to when the ball will cross the “hitting zone” from right in front of home plate to about the back point of the plate.

About the Knuckleball

Earlier we said the knuckleball could be called the fingernail ball. This is because the grip to throw a knuckleball involves digging the fingernails of 2 to 4 fingers straight into a seam or on the hide area. This grip makes the first and second knuckles of fingers stand out from the ball, making it appear the grip is all knuckles.

It’s not. The fingernails and tips push the ball on release, forward and over the top, to prevent the hard spin of regularly thrown balls. The result is a ball that does not spin, and again, aerodynamics get involved.

The ball not spinning leaves the seams, raised a tiny bit off the rawhide, fully out in the open to be gripped by air molecules (or breezes) along its path. The result is … unpredictable. Knuckleballs are said to float, bounce, or flutter like a butterfly. That is, they can move all over the place, and the pitcher most often has little control over how it will move.

All he can do is use his best skill to get it to bend and bounce through the strike zone, and hope all that movement avoids a bat head, or fools a batter into not swinging. The unpredictability of the knuckler means a lot of pitchers who depend on it are prone to bases on balls, if they aren’t on top of their game that day or if batters are patient.

It’s a reason why knuckleball pitchers are rarely late-inning relievers, when teams want to avoid baserunners at all costs. That’s also a reason why sliders are a preferred weapon for many closers: they can be as controllable as a fastball, and deadly effective when thrown correctly.

Injury Caveat

It must be noted that both the slider and curveball place tremendous strain on a human arm, namely on the elbow and shoulder, but also sometimes the forearms and wrists. These off-speed pitches could require rather violent snapping of the wrist upon release, which in turn stresses the joints up the road — the elbow and shoulder.

Most youth baseball coaches are keenly aware of the dangers of young players throwing these pitches too often, if at all. Some leagues ban their use until a certain level, like age 13 and up. Some fathers just flat-out forbid throwing them until the kid is even older. (Other fathers see dollars or college scholarships down the road and let a young kid throw his arm out with breaking balls).

Pro and college baseball history is full of cases where pitchers blew out arms and ended careers due to poor mechanics, genes, or other causes. It’s hard to blame any one action, but overuse of the slider and split-finger fastball, especially, and perhaps even the curveball, can be blamed for a lot of them.

Curveball vs. Slider – Here Are Difference