So far this year Roy Halladay, Adam Wainwright and Javier Vazquez have each provided a win’s worth of value with their curveballs alone. They have saved over ten runs with their curveballs. On the other end of the spectrum is Brad Penny, whose curveball has cost the Red Sox about a win (9.4 runs).

There is a lot that goes into determining the success of a pitch (speed, location, sequencing, delivery), but for a curveball movement is of the utmost importance. The movement of a pitch is how much the spin of the pitch causes it to deviate from a spinless trajectory, and is commonly broken up into horizontal and vertical components. So the vertical movement is how much a pitch sinks or rises compared to expectation based on its velocity, its trajectory and gravity. The horizontal movement is how much a pitch tails horizontally compared to expectation. Positive horizontal movement indicates a pitch that tails away from a RHB and in to a LHB.

Here are the movements of Halladay’s, Wainwright’s and Penny’s curves

(including Vazquez’s would make the graph too cluttered, but his fit in between Halladay’s and Wainwright’s). The gray dots are the movement of all curves for reference.

Halladay’s curve has a wide range of movement, but generally lots of horizontal movement (tailing away from RHBs an average of about 6 inches) and not much vertical break. Wainwright’s curve has lots of vertical and horizontal movement, sinking and tailing away from RHBs by almost 10 inches in each direction. Penny’s curve has little movement what-so-ever (his curves are very close to 0,0).

The two best curves have more movement than the worst one. I wanted to know if generally the more a curveball broke the better. Is it true that ‘flat curveballs’ get crushed? So I found the run value of a curve based on its total movement (a negative run value is better for the pitcher indicating runs saved). The gray lines are the standard errors.

The relationship is quite strong. As the movement of a curve increases so does its success. Not unexpected, but nice to see. Still you cannot predict curve success entirely on movement, there are many pitchers with worse curves that move way more than Halladay’s. But as a general rule the more one moves the better you can expect it to be.