Split-finger fastball
A split-finger fastball or splitter is named after the technique of putting the index and middle finger on different sides of the ball, or "splitting" them. This pitch is somewhat a misnomer since it is really an off-speed pitch. The split in the pitcher's fingers allows the use of the same arm speed in a regular fastball without generating the same velocity. The reason the pitch does not travel as fast is because the two "power fingers", the index and middle finger, which are typically on top of the ball at release, are now on the side of the ball, causing a degree of slippage and thus depriving the ball of, on average, 4-9 mph in velocity. The movement caused by using the split-finger grip is often described as the ball "dropping off the table", which can mostly be attributed to the more pronounced effect of gravity as pitch speed decreases, but is also aided by the degree of slippage upon release, which robs the ball of the tight, stabilizing spin characteristic of a fastball. This "sloppiness" of spin causes the ball to move somewhat erratically, in a similar fashion as a knuckleball, but not nearly to the same degree. Imagine throwing a frisbee without spinning it -- its movement would be erratic and somewhat unpredictable. A splitter, technically, is neither a breaking pitch, where movement is caused via the magnus effect by placing a tight spin on the ball, nor a fastball.
It is actually a changeup, and its movement often resembles other varieties of changeups, like the "Vulcan Change" made famous by closer Éric Gagné. A pitcher who throws a 95 mph fastball will probably have a splitter around 86-90 mph. A true change-up would be slower yet. The splitter was made famous by Chicago Cubs and St. Louis Cardinals Hall of Fame closer Bruce Sutter, who would be the first of many pitchers to make it the so-called "bread-and butter" pitch of his repertoire. Sutter claims that while he was in the Cubs' farm system, a minor-league pitching instructor named Fred Martin saw Sutter favouring his elbow. As Sutter was recovering from recent arm surgery, Martin encouraged Sutter to try throwing the split-finger pitch, reasoning it would place less duress on his arm.
The splitter is thrown today by many pitchers, including Roger Clemens, John Smoltz, Curt Schilling, and Hideo Nomo, a reflection of its popularity amongst power pitchers; Clemens's splitter, one of the tougher pitches in the history of baseball, has been a key reason for his continued success into his early to mid forties.(Along with performance enhancing drugs) This pitch also helped resucitate the career of former Houston Astros' pitcher Mike Scott; a journeyman starting pitcher prior to learning the split-finger, he won the National League Cy Young Award in 1986 after being taught the then relatively new pitch by coach Roger Craig. The split-fingered fastball also contributed to the success of former Chicago White Sox starting pitcher Jack McDowell (a.k.a. "Black Jack"), who won the American League Cy Young Award in 1993 and was a key pitch in the repertoire of former Detroit Tigers pitcher Jack Morris who finished with 254 wins.
Oakland Athletics right-hander Rich Harden has gained notoriety for his splitter, which features a bizarre knuckling action in midflight. It has been occasionally referred to as the "ghost pitch" and the "spluckle" (a portmanteau of splitter and knuckleball, coined by Harden teammate Adam Melhuse).
A related pitch is the forkball, which has even more of a tumbling action, because the ball is placed even deeper between the middle and index fingers.
