A Curveball is an off-speed pitch that can be valuable to any pitcher's arsenal, especially when it’s used in conjunction with a good fastball. It's a pitch that should look like a fastball spinning on the same axis but with topspin instead of backspin. The topspin causes the ball to drop rapidly and for players with a higher arm slot, it will move at more of a downward angle. It can fool hitters and induce weak contact or swings and misses. In this blog post, we'll dive into what a Curveball is, how to throw it, which pitch metrics are most critical to its success, and how pitchers can improve it.

What is a Curveball?

A traditional Curveball is a pitch that is thrown with various grips and the pitcher pulls down on the seams in front of the ball rather than staying behind the ball. The resulting movement of the pitch is typically a sharp, late-breaking downward movement, however, depending on the arm slot of the pitcher, the movement can have a mix of sink and glove-side movement.

We describe the spin direction of a pitch using the numbers on a clockface. From the perspective of a right-handed pitcher, the spin direction of a standard Curveball is downward between 7:00 – 7:45, with an arm slot in the 1:00 – 2:00 range. A high arm slot with a 6:00-7:00 spin direction is often referred to as a 12 – 6 Curveball. The higher the arm slot the more downward vertical movement of the pitch. The lower the arm slot, the more horizontal break on the pitch. 

The velocity and spin-induced movement of a Curveball is affected by the spin efficiency of the pitch. A high efficiency pitch has lots of top spin and slightly lower velocity because the last point of contact for the middle finger is on the front side of the ball closest to the catcher (Mental cue: show the catcher the back of your hand). A less efficient Curveball has greater velocity, but less spin induced movement as the ball spins a little more like a football, which is sometimes referred to as rifle- or gyro spin.

How to throw a Curveball

A Curveball is typically the first breaking ball that players learn to throw. The goal is to make the hitter think it’s a fastball by throwing from the same arm slot with the same arm speed as a fastball but creating movement with a higher spin rate and a spin direction opposite that of the fastball. 

Throwing a Curveball starts by knowing what you’re trying to achieve. However, if you are looking for lots of downward break, it will be difficult to do if your arm slot is ¾ or lower. 

The Grip is key:

The first step is to focus on exerting pressure with the middle finger. Begin with the middle finger running along the seam with the horseshoe of the seam facing up or down, whichever is most comfortable. To avoid putting pressure on the index finger, try keeping the pad of your index finger off the ball by having it hover off the ball, or curl the index finger so that the fingernail digs into the ball, or curl it more so that the last knuckle rests against the ball (knuckle-curve), or lay the index finger on top of the middle finger. The objective is to find a comfortable way to put all the pressure on the middle finger.

Don’t just rely on gravity for downward movement. Instead, think about trying to spin the ball, not just curve it. The goal is to have a high spin rate that creates downward, spin-induced movement. The more horizontal movement the ball has will result in a pitch more like a Slider or Slurve. 

In 2022, the MLB average spin rate on a 4-Seam Fastball was 2,274 RPM, while the average spin rate for a Curveball was 2,516 RPM, a difference of about 11%. However, a more revealing statistic is the spin rate to velocity ratio (SVR). You can use SVR to compare your own pitching compares to that of MLB players or anyone else. The SVR for a 4-Seam Fastball was 24.2 (2,274 RPM / 93.9 MPH), but the SVR for the average Curveball in 2022 was 31.7 (2,516 RPM / 79.4 MPH), a difference of about 31%! 

Experiment:

Experiment with different grips and different pressure points in catch play. Evaluate the amount of movement you get with each grip. Sometimes seeing the differences between grips will be obvious, but sometimes, a lower velocity can give the illusion of greater vertical break. The most accurate way to measure the amount of spin-induced movement is to use a device that measures speed, spin, and movement. An affordable and very accurate device to use for measuring your pitches is the pitchLogic baseball and mobile app by F5 Sports.

Critical Pitch Metrics for a Curveball

There are several critical pitch metrics that pitchers must pay attention to when throwing a Curveball:

1. Spin Direction: Curveballs typically have a more vertical spin direction. Think 6:00-7:45 for a right-handed pitcher or 4:15-6:00 for a lefty. Pitchers with lower-than-average arm slots are more likely to have Curveballs with spin directions outside of this range. 

2. Spin Efficiency: Curveballs can have a spin efficiency close to that of a 4-Seam fastball. The movement profile will vary based on the level of spin efficiency.

3. Arm Slot: It’s critical for the pitcher’s arm slot to remain similar to their fastball delivery. The most effective Curveball is hard to distinguish from a fastball.

4. Velocity: While a Curveball is typically slower than a fastball, it's still important to have enough velocity to give the appearance of a fastball and create a late, sharp break.  

5. Movement: The movement of a Curveball refers to how much the ball breaks or curves as it approaches the plate. A good Curveball should have movement that fools the hitter into chasing a pitch out of the strike zone and swinging over it, or taking a strike that the hitter thought was going to be a fastball out of the zone (back door or front door Curveball).

6. Location: Finally, the location of a Curveball is critical for success. An ideal Curveball should appear headed for the strike zone and then break down and away, which can induce swings and misses. Another approach would be for the Curveball to start out of the zone and break to the inside or outside corner of the strike zone. Those thrown in the center of the strike zone (hanging Curveball) are more likely to be hit with high exit velocity.

How to Improve Curveball Movement

If you're looking to improve the movement of your Curveball, there are several techniques you can try:

1. Adjust your grip: Experimenting with different grips can have a significant impact on the movement of your Curveball. For example, experiment with moving your index finger to concentrate the pressure on your middle finger or move the ball farther out toward your fingertips or back closer to the palm of your hand. It has to be comfortable for you.

2. Adjust your release: Focus on having the back of your hand visible to the catcher to create more top spin. Alternatively, focus more on throwing the ball like a football to increase velocity and more rifle- or gyro spin.

3. Alter your arm slot: Changing your arm slot can also affect the movement of your Curveball. A lower arm slot can produce more horizontal movement, while a higher arm slot can result in more vertical movement. This adjustment should only be used sparingly. A small arm slot deviation from your fastball (maybe 30 minutes on the clock face) may be difficult for a hitter to detect, but a large difference will make it easy for hitters to see your Curveball coming.

4. Use STUFFpL for personalized recommendations: Each pitcher has different strengths and weaknesses. Your ideal Curveball depends on a variety of factors, including your arm slot, how it pairs with your fastball, and your ability to create spin. STUFFpL is built into pitchLogic and can help you determine which adjustments are right for you.

5. Practice, practice, practice: Ultimately, the key to improving the movement of your Curveball is practice. During flat ground and catch play, work on adjusting your grip, arm slot, and release point to get the movement you want. As you get more comfortable, start using it in bullpen sessions to master the pitch. 

A Curveball can be a great addition to any pitcher’s arsenal. To get the best results, focus on one metric at a time, because they are all related. For example, a lower arm slot will increase horizontal movement but can also affect your spin efficiency.

By paying attention to critical pitch metrics such as spin rate, velocity, movement, and spin efficiency, and the techniques that enhance them, you can improve the movement and effectiveness of your Curveball. Remember, practice makes perfect, so keep throwing that Curveball and watch the hitters’ knees buckle!