I have a serious question here.  What causes the late break on a pitch that analysts are always talking about?  A pitch leaves the pitcher's hand with a certain spin rate and velocity which determine the size and direction of the break.  If a pitch is to start breaking more during its flight, it can't be because the spin rate increases; if anything, the spin rate will decrease slightly during its flight.  That would actually cause it to break less. Contrariwise, the velocity of a thrown ball will decrease slightly during its flight because of air resistance.  That slower speed would cause it to break slightly more because of less inertia.  So the two effects would seem to even out.

What then, is the cause of the late break, or is the late break effect an illusion of some sort?

My uneducated opinion, but it probably has to do with the acceleration from gravity causing the downward velocity to be faster the longer it is airborne, combined with the drag caused by the spin on the ball. 

I think it’s usually spider-tack causing it. 

The Physics of a Curveball

Physicists would argue that the late break is an illusion. That there are no forces that could account for such an abrupt change in the Magnus Effect. In fact the slowing forward velocity and rotation due to drag should decrease the effect.

Basically if you have ever thrown a curve you know how it works. A good curve ball is thrown with an amount of finger pressure and snapping the wrist. This will impart some amount of side spin and backspin .Basically the mound is just the right distance from the plate for the spin to take effect. While it spins the minute it leaves your hand it takes a split second for it to react against the air surrounding it. The same thing applies on a batted ball going to the opposite field or a golf ball when it slices.

Now it obviously takes time to perfect the pitch and pitchers do experiment with different ways to throw it to find whats best for them as far as release point and the amount of break and when it breaks, that feels best for them and can be delivered with the most consistency. Some pitchers can throw a curve a number of ways with varying amounts of speed and spin. I'm sure you have heard the term " a get me over curve or fastball", Or a big breaking curve as opposed to a sharp or late breaking curve. Usually the difference with those are the speed the pitch is thrown. Slower curves will break earlier and has a bigger arc because they take a smidge more time to reach the plate so the spin takes effect earlier.

I don't know if I truly answered your question. A pitcher who throws them well and with consistency has put in a lot of hours playing around with the pitch in every way possible. Lower seams and slicker balls make it even harder which is one reason so many pitchers started using spider tack besides the obvious reason of getting more spin.

 

This is from a 1998 paper. There are lots of versions of it in various formats. The upper chart is "as if you were looking down on the pitch", the lower chart is "watching the pitch from the side". 16 meters is just over 48 feet, so the pitch would be thrown about 12 feet off to the right of this chart. 

To get the late break on a curveball you need 2 things. You need the ball to have a spin on it that interacts with the wind - that is what deflects the pitch gradually to the side. You also need the pitch to hit the "peak" of its trajectory at the right point - if the peak comes too late, the pitch won't break enough and it will become a hanger. If you have the peak at the right spot, then the pitch will be accelerating downwards as it approaches the batter and that will give you the impression of a late break downwards, because it has been moving down but because the speed increases enough for your eyes to see it just as it passes the plate.

https://www.researchgate.net/figure/1-Simulated-curve-ball-trajectory-The-solid-line-represents-the-normal-gravitational_fig25_241376252

I can't define "late break", but I know it when I see it.