Major-league baseball pitchers usually throw fastballs, curveballs, and off-speed pitches. A few brave souls, however, have made a career out of throwing the knuckleball. The pitch entails lobbing the baseball in such a way that it doesn't rotate, and therefore moves in a manner that's impossible to predict. The filmmakers follow Tim Wakefield and R.A. Dickey, the only two knuckleball pitchers in the majors during the 2011 season, as they attempt to stay in the big leagues while relying on this unorthodox weapon.
by Perry Seibert synopsis