Now that I've seen this clip, (or re-seen this clip, I saw the movie on TV decades ago), I realize that the meaning is tied up with his gesture. Modzelewski was clearly a pitcher, who throws the ball. All pitchers have a variety of styles of pitch, foremost a fastball, which is simply thrown too fast for the batter to hit, and the curveball, which goes straight until the last moment before it reaches the batter, then curves down and to the side. There is another pitch called the screwball, which curves to the opposite side from the normal curveball, which very few pitchers can master. By the way, these pitches actually do curve, it has been measured scientifically, it is not an optical illusion as some have held in the past.
Clearly the impatient juror was referring to Modzelewski's curve ball or screwball as indicated by his gesture. He meant that Modzelewski threw a very good curveball or screwball, or both, and was very hard for the batters to hit. By the way, I should mention the pitcher's job is to prevent the opposing batters from hitting his pitches, at least not very much.