Noun
knuckleballer (plural knuckleballers)
(baseball) A baseball pitcher known for throwing knuckleballs.
While teams with a knuckleballer on their pitching staff often employ a special "knuckleball catcher" who is equipped with a knuckleball mitt, similar to a first baseman's glove, it is still extremely difficult to catch. Source: Internet
There tends to be a higher incidence of passed balls when a knuckleballer is pitching. Source: Internet