Graph of the Day: Wang's Spin Movement at Home

by Harry Pavlidis on May 30, 2009 12:24 PM EDT

If you're saying Chien-Ming Wang's sinker has lost many inches of movement, you'll also have to say he used a screwball in 2008. Or you can just say that Yankee Stadium was wrong in 2007, adjusted too much for 2008, and again at the new park in 2009. Based on the slider movement, it's still off.

That makes it hard to tell what's changed with Wang without adjusting the base data. That includes the release points, the initial acceleration and velocity values.

Bonus graph: lateral acceleration (ax) from Yankee Stadium(s) from 2007 thru 2009.

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So you're saying we shouldn't trust pitch f/x data at face value...

Beyond the Boxscore // Calling BJ Upton lazy is lazy.

by Sky Kalkman on May 30, 2009 2:31 PM EDT reply actions

What is lateral acceleration

St. Louis Cardinals... defying win expectancy since 2008

by vivaelpujols on May 30, 2009 4:15 PM EDT reply actions

I was about to ask that question.

Rebuild and Restock.

by trademaker on May 30, 2009 5:02 PM EDT up reply actions

Sidways movement, sort of.

Not measured in absolute distance moved, but instead the amount of sideways acceleration caused by the force caused by spin.

Beyond the Boxscore // Calling BJ Upton lazy is lazy.

by Sky Kalkman on May 30, 2009 5:05 PM EDT up reply actions

Gotcha

St. Louis Cardinals... defying win expectancy since 2008

by vivaelpujols on May 30, 2009 5:12 PM EDT up reply actions

So is his graph all pitchers in Yankees stadium or just Wang?

St. Louis Cardinals... defying win expectancy since 2008

by vivaelpujols on May 30, 2009 5:16 PM EDT up reply actions

Can't just be Wang with how many data points there are.

Pretty sure each vertical line of dots is one game or one start.

Beyond the Boxscore // Calling BJ Upton lazy is lazy.

by Sky Kalkman on May 30, 2009 5:19 PM EDT up reply actions

All pitchers

to show the shift

by Harry Pavlidis on May 30, 2009 6:41 PM EDT up reply actions

Not quite

It’s the rate of change of speed in the lateral direction (x-axis in pitchf/x). Magnus force causes spin movement. Based on where the PITCHf/x system thinks the release point, and where it’s going in the initial flight, the acceleration values are estimated and used , along with velocity and location, to create the estimated path of the pitch. If the cameras are off, the initial values will be off to force the ball on path to home plate. Ike Hall has some coherent work on the topic. I’m just an unfrozen caveman baseball nerd.

by Harry Pavlidis on May 30, 2009 6:43 PM EDT up reply actions