A split-finger fastball, or a splitter, is a baseball pitch thrown like a fastball with an v-shaped split finger grip. When thrown correctly, it moves like a fastball, straight in the air, but suddenly drops as it approaches the home plate. Here is a gif of how the pitch moves.
I've searched various sources that explain the reasons, which aren't very convincing to me:
Reason 1: The ball has a reduced backspin as compared to a regular fastball, and hence falls due to a stronger gravity than the upward Magnus force.
This does not convince me. This scenario should result in a constant force on the ball throughout it's path of motion, and the descent should be gradual, and not be seen at the end of the pitch.
Reason 2: The slight backspin on the ball forms ripple vortexes as it travels through the air, which eventually leads to the ball developing a topspin, which causes the ball to drop
This reason seems to be more plausible, and can explain why the ball drops suddenly and not gradually. However, I'm not so convinced if this is a very accurate reasoning or not. A pitch known as the knuckleball, thrown with very little spin, utilizes these vortices to make the ball move unpredictably. I'm not certain if the slight backspin allows the pitcher to control the effect these vortices have.
What is the most accurate explanation for why a splitter moves the way it does?
Best Answer
It certainly does not have topspin at any point. The first reason is correct. It has less backspin and therefore appears to drop. The camera angle from behind the pitcher is deceiving. Although it appears to drop off suddenly, it is more gradual than it appears. A straight fastball defies gravity quite a bit, as does a split fingered fastball, because they both have backspin. The splitter just does not defy gravity nearly as much. The best splitters have relatively high velocity to mimic a fastball, but reduced backspin to get the “drop” action.