iayork said:
That said, Brooks also shows his last game to have good vertical movement. Just a quick eyeball of the numbers doesn't show a really obvious correlation between his vertical movement and success, but it certainly seems like it can't hurt.
Thinking about this later, I realized it is
exactly backward.
Because sinkers are fastballs, and are thrown with backspin, their vertical motion is a rise, relative to the path they'd take with no spin (i.e. relative to pure gravity). The four-seam fastball is thrown with more or less pure backspin, and mostly "rises"; its vertical movement is a relatively large positive number. A curve, thrown with no backspin or ideally with front spin, actually drops relative to gravity; its "vertical movement" is a negative number.
The sinker is a fastball, but thrown so that the spin axis is less purely backspin, but it still has considerable backspin. Sinkers therefore rise relative to gravity, and have a positive vertical movement, but they rise
less than a four-seam. The "sinking" action is a double illusion -- because hitters expect a fastball, and compensate for the rise that they're used to, they swing over the sinker.
So for a two-seam fastball, you're not looking for a large vertical movement component, you're either looking for a small vertical movement, or (more likely to be effective, I guess) you're looking for a reasonable amount of separation between the rise of a four-seam and the rise of the two-seam.
So the fact that Porcello's two-seam had lots of vertical movement the other day actually means it had
less sink than normal, and it actually had much less separation from his four-seam that day too (in terms of vertical movement, anyway).
So we're back to the fact that he was very effective even though he didn't throw an extraordinary number of two-seams, and his two-seam was less sinker-like than almost any other game this year.
Again, I think his location was the key.