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knuckle ballor knuck·le·ball (nŭk′əl-bôl′)
A slow pitch that has almost no spin and veers erratically, thrown by gripping the ball with the nails or knuckles near the tips of the index and middle fingers, and often the third finger.
American Heritage® Dictionary of the English Language, Fifth Edition. Copyright © 2016 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.
(Baseball) a throw in baseball that flies in an erratic way and is difficult to hit well because the pitcher holds the ball between the fingertips or knuckles
Collins English Dictionary – Complete and Unabridged, 12th Edition 2014 © HarperCollins Publishers 1991, 1994, 1998, 2000, 2003, 2006, 2007, 2009, 2011, 2014