http://www.oddball-mall.com/knuckleball/k101.htm
Looks like "knuckleball" is the name of a family of pitches. Supposed to be a
slowly rotating ball.
The reaction of the air behind the ball causes the motion.
That slo-mo of Wakefield knuckler last night was simply amazing. It takes a lot of courage to toss that floater and hope for the best.