Screwball pitches dont get as much ink as they once did. A curveball from a right handed pitcher will break right. A screwball from a right handed pitcher will break left. As you might understand from that description alone, it is much harder to have a ball break the opposite direction from where your arm is coming down.
Screwball pitches are aptly named. To throw a screwball, you have to twist your arm and hand counterclockwise. Just the motion alone is fairly awkward, let along throwing a ball towards a pre-determined spot. A screwball can be very hard on the wrist. It can be difficult to combine with other breaking pitches.
Theres a reason that pitchers often perfect one type of pitch. There are knuckleball pitchers, forkball pitchers, and screwball pitchers. Of course, these pitchers will also have a fastball and a changeup. It is a rare pitcher who has five or six pitches in his arsenal. It is rarer still to find a pitcher who has perfected every pitch. Its what separates a fifth starter from an ace.
Mistaken Screwball Pitches
In some way you could consider a cut fastball, or a cutter, to be sub-par screwball pitches. Obviously this isnt giving enough credit to the cutter, which can be an enormously effective pitch. At times, though, a cutter which breaks right can seem like a light screwball. A true screwball will break dramatically.
