In baseball, a curveball is a particular type of pitch that's thrown with a specific type of grip on the ball and is such that the forward spin impacts the actual movement of the ball in a downward path that is impacted by its pitching velocity. There are always subtle differences between the pitches thrown by various pitchers and a curveball by one pitcher will likely not be very much like the curveball thrown by another. A curveball is gripped by the pitcher much like a cup or drinking glass would be held with the pitcher placing his middle finger parallel to one of long seams.