The knuckle-curve is one of baseball's greatest paradoxes, given that a curveball is defined by its spin and a knuckleball is defined by its lack thereof. Still, the knuckle-curve produces the desired effect of the two pitches -- a slow, curveball break mixed with the unpredictable fluttering of the knuckleball.
Very few pitchers have mastered the knuckle-curve, and those that throw it generally don't do so often. It's a deceptive weapon for those pitchers, often stashed away until they think a hitter will be fooled by it.
There are a few different ways to grip and throw a knuckle-curve. The basic premise is that at least one of the pitcher's fingers is bent while holding the ball -- like a knuckleball -- while the pitcher maintains the snap of the wrist that is synonymous with a curveball.
Think of the pitch as a spectrum between a knuckleball and a curveball. For pitchers who emphasize the curveball aspects of the pitch (bending one finger so that a knuckle is on the ball), a knuckle-curve is basically just a curveball that spins and moves slower. And for pitchers who emphasize the knuckleball aspects of the pitch (gripping the ball like a knuckler, while ever-so-slightly snapping the wrist), a knuckle-curve is basically just a knuckleball that spins more and moves faster.
Because some knuckle-curves are so close to a regular knuckleball and others are so close to a regular curveball, the pitch has existed for years while simply being indentified as one or the other. It's quite possible that Ed Summers, who pitched for the Tigers until 1912, was the first to throw the knuckle-curve regularly, as he was well known for the varied deliveries and movement on his knuckleballs.
Watch: Edinson Volquez strikes out Brett Lawrie on a knuckle-curve.
In A Call
"slow curve," "fluttering curve," "dry spitter"