THE BOOK--Playing The Percentages In Baseball

Nice summary, Harry. 

Something new that’s not in Gameday itself has appeared in the Gameday XML data files—spin rate and spin direction. The spin direction data appear to be corrected for release point, so the values reflect spin from grip and release action rather than arm slot. Combined with start speed and/or RPM, these values can be of great importance in post hoc classification. Many PITCHf/x aficionados already calculate and use these values on their own, but now they are available for everyone.

As you note, many of us have been using spin and spin direction already.  I have not yet had a chance to check out these numbers.  However, I suspect that the spin direction is calculated in the manner discussed several years ago by me, Mike Fast, and others.  See http://webusers.npl.illinois.edu/~a-nathan/pob/Analysis.pdf.  The spin direction is determined by the spin-induced break, which determines the direction of the Magnus force in the x-z plane.  The spin direction is rotated 90 degrees from the direction of the Magnus force.  If there is a y component to the spin, as is often the case for a slider, there is no Magnus force due to it and it therefore has no affect on the trajectory and cannot be determined.  Therefore, this technique only determines the direction of the projection of the spin in the x-z plane.  However, with that proviso, it does determine the spin direction very accurately.  The ball is spinning however it it spinning, and there is no need using this technique to correct for release point.  The magnitude of the spin is, once again, only the magnitude in the x-z plane.  It is determined from the size of the deflection, which determines the so-called lift coefficient CL.  The spin is determined from an approximate relationship between CL and the spin.  So, unlike the spin direction (x-z plane only), the determination of the spin magnitude is only approximate.

I saw the spin angle and rate added to the pitch description, but in spot checking the xml files of a couple games I wasn’t able to find any hit f/x data. Is it being recorded yet? If I overlooked it, what files contain the data?

Brian, the HITf/x data comes from the same camera video that produces the PITCHf/x data, so it has been and is being recorded.  It’s not available yet, but when it is, I believe Sportvision intends to make it available for past games as well.

Yes, I can confirm what Mike has said.  The technique for extracting the hit ball information from the video is being perfected.  What I don’t know is the manner in which the hitf/x data for past games will be made available to the public, once the data have been obtained.

Sportvision and MLBAM have announced the Second Annual PITCHf/x Summit to be held in San Francisco on July 11, 2009. You can find more details and April 2009 HITf/x data for download (registration required) at the Sportvision site:
http://baseball.sportvision.com/summit