NOTE: The conclusions drawn in this post are based on an erroneous idea about the orientation of this pitch. For the correct ball orientation, this description does not make sense.Â ForÂ aÂ betterÂ explanation,Â seeÂ theÂ newÂ postÂ
Before I get started, first I want to acknowledge the influence or Rod Cross’ article on this topic. He says the same things, but without focus on pressure gradient. Also, if you haven’t already, it would be helpful for you to read my post on boundary layers and the post on seams and pressure gradients.
The idea of a “Laminar Express” is to cause the flow on one side of the ball to be laminar, and thus have an early separation from the ball surface, while the other side is turbulent and has a later separation. The difference in these separations would cause a lateral force on the ball.
I’ve sketched the situation below. The pitch requires a 2-seam orientation, which produces large areas of smooth surface on the two sides of the ball. A small component of “gyro” spin (which results in the axis being tilted in this sketch) is necessary to move one seem on the front of the ball forward. As I pointed out in the pressure gradient post, if a seam is near the front of the ball, it will disturb the boundary layer, but it will return to smooth, laminar flow because of the strong, favorable pressure gradient there. This is the case for the seam on the first base side near the front of the ball. The seam on the first base side near the back has no impact, because the boundary layer has already separated there.
On the third base side on the front of the ball, there is a seam near the hemisphere (vertical grey line) that delineates favorable from unfavorable pressure gradient. The favorable gradient here may not be strong enough to damp out the disturbance of the seam, so the flow becomes turbulent, and remains attached to the ball longer.
This is all speculation on my part. Many claim to have seen this effect and it is normally detected through Rapsodo data that are incorrect (this device predicts ball path based only on Magnus effect and cannot account for the effect of an asymmetric waked due to a different boundary layer state on two sides of the ball.)
Obviously, if this description is correct, executing this pitch relies on being able to orient the ball axis and seams precisely. No other pitch in baseball (that I know of) depends on the seam orientation after the ball is released.