THE BOOK--Playing The Percentages In Baseball

Tuesday, January 31, 2012

KNUCKLEf/x

By Tangotiger, 11:42 AM

From Alan:

Within the precision of the tracking data, knuckleball trajectories are just as smooth as those of ordinary pitches. Read on to find out how I arrived at this conclusion.
...
With apologies to John Walsh, I conclude that knuckleballs are more like bullets than butterflies.

How about it’s more like bullets fired by a 10-yr old? So, the kid doesn’t have good aim, he’s jittery when he fires, and ask him to rehit the same target, he won’t be able to. So, it follows a smoothish pattern, after the fact, but even upon release (knowing angle of release, speed, spin angle), you won’t be able to predict that path.

That about right?

• Sabermetrics • Ball_Tracking

#1 (see all posts) 2012/01/31 (Tue) @ 12:21

Yup!

#2 Peter Jensen (see all posts) 2012/01/31 (Tue) @ 13:02

Alan - You don’t actually know what the spin on the knuckleballs was do you? Aren’t you best fitting some of the parameters of your model to the actual location data do give a probable spin rate and direction?

#3 (see all posts) 2012/01/31 (Tue) @ 13:19

Peter: no, the spin is not known. The fitting determines the “lift coefficient” C_L. If it were an ordinary pitch, the C_L would be related to the actual spin. In fact, the relationship between C_L and the spin is known (albeit only to abut 20%) experiementally, and it is that relationship that is the source of the spin rate in the PITCHf/x data (i.e., it is only an estimate). For the knuckleball, C_L is simply a number that characterizes the strength of the transverse force on the ball. The fitting also determines an angle (call it phi) that characterizes the direction of the force. For ordinary pitches, if you take phi and add 90 degrees, you get the spin axis.

Page 1 of 1 pages

<< Back to main

THE BOOK--Playing The Percentages In Baseball

Tuesday, January 31, 2012

KNUCKLEf/x

Latest...