Definition of "knuckleball"

knuckleball

noun
plural knuckleballs
1. (baseball) A pitch thrown with the ball gripped on the fingertips and released with no rotation, which travels over an unpredictable path to the plate due to micro-turbulence in the air.
2. (figurative) An event that is hard to predict.
verb
third-person singular simple present knuckleballs, present participle knuckleballing, simple past and past participle knuckleballed
1. (intransitive, baseball) To pitch knuckleballs.
  Quotations
  Varitek did not start so Kevin Cash could catch the knuckleballing starter Tim Wakefield.
  2008 April 16, The Associated Press, “Tigers Rally Again to Defeat the Twins”, in New York Times‎