In this motion plot, the two circles represent the flight of two pitches. The blue circle is the average pitch flight of Colon’s two-seamer in two-strike counts, and the red circle is a theoretical straight fastball thrown from the exact same release point. It’s important to note that by “straight” fastball, I mean literally, no horizontal movement whatsoever, so the effect here is somewhat exaggerated. The dotted box is the strikezone. Depth of the pitches is indicated by the size of the circles, where the circles are largest at the release point and smallest when they reach home plate. This is from the catcher’s perspective.
As you can see, the two pitch flights are very close until it’s too late for the hitter. The paths of the two pitches visibly separate only when they are already close to the plate. Compared to real life, the plot is slowed down by a factor of 20, so it’s hard to imagine how major league batters can tell the difference between the two pitches. The movement on Colon’s two-seamer keeps it within the strikezone, while the straight fastball whisks past the outside corner for a ball. Pretty darn nasty.