What is a Curveball? Definition, Grip, and Example
A curveball is a slow breaking pitch thrown with heavy topspin that drops sharply as it crosses the plate, typically 70-82 mph in MLB.
What is a curveball in baseball?
A curveball is a slow, sharply breaking pitch thrown with heavy topspin that tumbles downward—and usually glove-side—as it crosses the plate. In MLB it lives in a velocity band of roughly 70-82 mph, 10-15 mph slower than a starter's fastball. The pitch is built on grip and wrist action: the pitcher tucks the middle finger against a seam and the thumb on the opposite seam, then snaps the wrist downward at release to impart pure top-to-bottom rotation. That rotation creates Magnus force that pulls the ball down faster than gravity alone, producing the dramatic late drop hitters describe as "falling off the table."
How a curveball is measured
Statcast tracks every curveball thrown in MLB and breaks it into five core metrics:
- Velocity: 70-82 mph for starters; power curves touch 85+
- Spin rate: elite curves spin 2,700-3,200 rpm; the league average sits near 2,500 rpm
- Spin axis: a true 12-to-6 curveball has an axis near 6:00 (pure topspin); most modern curves are 7:00-8:00 (top plus gyro spin)
- Induced vertical break (IVB): the drop in inches caused by spin alone, separate from gravity. Quality curves show -8 to -16 inches of IVB
- Horizontal break: 5-15 inches glove-side movement on a typical 12-6 or 11-5 curve
Total observed drop on the broadcast graphic combines IVB plus the gravity drop from the slower velocity, which is why a curve can look like it falls 50-60 inches.
Worked example: Charlie Morton, 2023
Morton's curveball was the most-thrown breaking ball in MLB at 41.6% usage. Average velocity 79.4 mph, spin rate 2,892 rpm, with roughly 55 inches of total vertical drop on Baseball Savant. Hitters whiffed on 36.1% of swings and slugged just .288 against it. The pitch generated the majority of his 183 strikeouts that season—a textbook example of a single elite curveball anchoring an entire arsenal.
Why curveball quality matters
Front offices grade curveballs on the 20-80 scouting scale; an elite curve grades 70+. The pitch is the league's best put-away weapon in 0-2 and 1-2 counts because the velocity gap from a fastball makes timing nearly impossible when located below the zone. It also produces ground balls when contact does happen, since the steep downward plane forces hitters to swing over it. Pitchers without an above-average breaking ball rarely project as starters at the major league level.
Limitations and common misconceptions
A curveball is not a slider. Sliders break harder horizontally with less vertical drop and run 5-10 mph faster. A sweeper is a slider variant with extreme lateral movement and a near-horizontal spin axis. A knuckle-curve—thrown by Craig Kimbrel and Phil Hughes, among others—is a curveball gripped with the index finger curled against a seam, often producing higher spin efficiency. The "12-to-6" descriptor is rarer than fans assume; most modern curves break diagonally.
Curveballs also carry elevated elbow stress relative to fastballs, which is why coaches limit their usage in young arms. And a slow curve thrown without command gets crushed—shape alone does not produce outs.
Related terms
In Legends Deck
Every pitcher card carries a separate breaking-ball quality rating derived from Statcast spin rate, induced vertical break, and observed whiff rate on curveballs. Two pitchers with identical strikeout totals can field very different curveball ratings—and very different in-game outcomes—when one's pitch generates 35% whiffs and the other's only 18%.