The Physics of “Late Break”

There are a couple of persistent myths about pitching that are finally on the wane.  Since the early days of baseball, many have argued that curveballs don’t actually curve but just appear to do so.  Another legend is the rising fastball.  Thanks to technologies like PITCHf/x and Statcast, we now know these two tales, while charming, are simply folklore.

In this article, I hope to add “late break” to this collection of pitching fairy tales.  I guess I should be more careful.  I don’t want to say “late break” doesn’t exist but instead try to convince you that all break is late break. The term “late break” is simply redundant.

This point has been addressed by others including the founding father of physics and baseball.

Does a curve ball then travel in a smooth arc like the arc of a circle? Yes. Does the ball “break” as it nears the plate? Yes.  Neither the smooth arc nor the break is an illusion but a different description of the same reality.”
— Robert Adair, The Physics of Baseball

To begin to understand what I mean by “all break is late break,” I’m afraid I need to ask you what I’m sure you’ll say is a “trick question.”  At the right is a sketch of a pop-up on a planet where they play baseball, but there is no air to interfere with the behavior of the ball.  So, the ball is only under the influence of the gravitational force. 

In the sketch, I have labeled the position of the ball every half second during its flight.  The red arrows are the velocity at two of the positions.

The question:  Compare the size of the gravitational force at each image of the ball.

Think about it for a minute before I give you the answer, even though you won’t like it…The gravitational force exerted on the ball is the same throughout the entire flight!

You probably said the force dropped as the ball went up and the force at the very top of the flight was zero–most people do.  That’s because people often confuse the force on an object with the motion of the object.  Force and motion are related, but very distinct, concepts.  The speed of the ball actually is the largest at the bottom and drops to zero at the top, but that is the speed of the ball, not the force on the ball.

Why is this confusion so common?  I suspect it is because we all know the force on an object is intimately connected with the motion of the object.  The connection between force and motion is Newton’s Second Law, which says that the force on an object isn’t responsible for the motion of the object, but instead the force causes changes in the motion of the object.

Let’s use this idea to focus on just the fall of the pop-up as shown at the right.  In the images at the right, I have indicated the forces as green arrows and the velocity of the ball as red arrows.  Notice the green arrows at each image are the same size, while the red arrows grow as the ball falls and speeds up.

Notice that the force, while itself unchanging, is constantly changing the motion of the ball.  That is, the ball speeds up as it falls, and the distance it travels during each half-second interval increases. The increase in distance is pretty small between the top two images of the ball and relatively large between the bottom two images. So, force changes the motion of the ball, but it takes some time for these changes to accumulate and become dramatic.

Now that we’ve mastered how force and motion work for pop-ups, let’s apply the same idea to a pitch on the airless planet.  Below, is a sketch of a pitch only influenced by gravity.

The ball is shown about every 0.05 seconds as it travels from right to left on its way from the pitcher to the plate.  The constant gravitational force (green arrows) pulls downward on the ball, changing the ball’s motion.  After all, if gravity wasn’t doing its thing, the ball would just stay at the same height moving along the black dashed line.  So, the blue line is the trajectory created by all the accumulated changes in motion caused by the gravitational force.

Here’s the point.  Since the time intervals are so short for a pitched ball, it takes quite a large fraction of the flight time for the changes caused by the force to accumulate to the point where the hitter can distinguish between the motion without any force and the motion under the influence of the force.  From this sketch, it appears that it takes nearly half the flight time for the ball to deviate significantly from the no-force trajectory.

So essentially, all break is late break.  There is little deviation in the motion of the pitch early in its flight, and the largest changes in motion occur as the pitch nears home simply due to the basic physics of Newton’s Second Law.  Hence the term, “late break” is redundant if not completely wrong.  That is to say, all break is late break.

Now, let’s head back to Earth, where there is plenty of air and everyone has played enough slow-pitch softball to easily compensate for the change in motion of the pitch due to gravity.  After all, gravity works the same way regardless of whether the pitcher throws a fastball, slider, curve, or change.  So, dealing with gravity isn’t a big issue for hitters.

As explained many times before in many places, the air exerts forces on a pitch that depend upon the speed and spin of the ball.  The batter has little idea as to the speed or spin of the ball during the initial motion of the pitch.  In addition, the forces the air exerts will not have had enough time to accumulate to the point change in the motion of the ball will give the batter much of a hint.

So, the trick to having highly effective “late break” is to disguise the speed and spin of the pitch from the batter for as long as possible.  The most common way this works is for pitchers to deliver their different pitches with identical deliveries and similar early trajectories.  This idea is called tunneling.

This is also Alan Nathan’s argument, which he described in terms of trajectories and batter perception when he examined the secret to Mariano Rivera’s success.  Rivera’s cut fastball is so effective because “all break is late break.”

Well, it’s time for me to give you a break, though that’s probably a little too late.  I’ll conclude by sharing some thoughts of Nobel Prize winner Richard Feynman regarding the beauty of a flower.  Instead of just stealing the quote, I modified it to my devious ends.

I have a friend who’s an artist a pitcher and has sometimes taken a view which I don’t agree with very well. He’ll hold up a flower throw a pitch and say, ‘Look how beautiful it is,’ and I’ll agree. Then he says, ‘I, as an artist a pitcher, can see how beautiful this is, but you as a scientist take this all apart and it becomes a dull thing,’ and I think that he’s kind of nutty…science knowledge only adds to the excitement, the mystery and the awe of a flower pitch. It only adds.”