Re: Tony Cingrani #12 on the BA Hot Sheet this week
A cutter is a held like a four seam fastball but a bit off center in the fingers and breaks away from the hitter (RH pitcher vs RH batter) as it reaches the plate. Its a fastball really but with a slider action. It's late "cut" and high velocity makes it murder on hitters. And if you're the unlucky off handed batter facing the pitcher using it, the pitch can literally crack your bat right in your hands.
A screwball is thrown with a grip similar to a curve, usually by lefties, with a reverse break of the wrist to the curve. Carl Hubbell threw it so often it permanently turned his forearm inward even after his retirement. Because of the ligament structure of the forearm's bones the reverse pronation is extremely hard on the arm and that's why it is rarely used. It's very effective but it's an invitation to arm problems, too.
The split finger fastball is held between the fingers but the fingers are spread and snapped down across the ball and the forearm pushed forward producing a nasty sudden drop at the plate. Clemens used it late in his career. It was taught by pitching coach Roger Craig who thought it would help pitchers with arm problems but there is a lot of back and forth about that. Some say it isn't any worse than any other pitch and some say its really tough on pitchers arms. It's nasty but fairly difficult to learn to throw correctly. I think the reason its seldom used anymore is that the debate has pretty much come down on the side of it damaging arms althogh Bruce Sutter used it for most of his career.