As a noun knuckler is
(baseball) a knuckleball.
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Not English
Wikidiffcom has no English definition. It may be misspelled. knuckler
English
Noun
(
en noun)
(baseball) A knuckleball
See also
*curveball
*slider
*fastball
*cut fastball
*two-seam fastball
*split finger fastball
*sinker
*screwball