: a baseball pitch made by gripping the ball with the knuckles or fingernails of the index and second and sometimes third fingers pressed against the top of the ball and thrown usually with little speed or spin so as to give it a typically erratic course
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Baseball.
a slow pitch that moves erratically toward home plate, usually delivered by holding the ball between the thumb and the knuckles of the first joints of the first two or three fingers.
[1905-10, Amer.]
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knuckle ball,
Baseball. a slow pitch thrown from the knuckles and the heel of the palm, remarkable for its curving in several directions or dropping abruptly at the end of the delivery: ยป
A knuckle ball does not spin, but floats toward the plate and then either darts to one side or sinks or does both (New York Times).
Useful english dictionary. 2012.