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October 23, 2010

BP Unfiltered

PitchTrax Wrong, Not Ump

by Mike Fast

Normally the PitchTrax data shown on television is pretty accurate, within an inch or so of reality.  It's based on Sportvision's PITCHf/x pitch-tracking camera system, which usually does a great job.  Not so in Friday's game.  You might have thought home plate umpire Brian Gorman had lost his bearings around home plate.  However, in this case it was the PITCHf/x camera that was lost.  According to my calculations, the horizontal plate locations reported by PITCHf/x in Game 6 of the American League Championship Series were off by about 5-6 inches toward the third base side of the plate.  

I calculate this offset by comparing where pitchers have located their pitches to left-handed and right-handed batters throughout the past few seasons to where the pitchers located their pitches in the game under consideration.  For one pitcher, the comparison may not be very helpful, but when aggregated across all the pitchers who appeared in a game, this method tends to be fairly accurate, within an inch or two at the game level, and better than that if you average a few games together.

Here are all the horizontal offsets calculated by this method for each League Championship Series.

-0.1 inches, Citizens Bank Park, Game 1
-0.0 inches, Citizens Bank Park, Game 2
 
-1.7 inches, AT&T Park, Game 3
-2.5 inches, AT&T Park, Game 4
-1.8 inches, AT&T Park, Game 5
 
-1.9 inches, Rangers Ballpark, Game 1
-2.7 inches, Rangers Ballpark, Game 2
 
-0.5 inches, Yankee Stadium, Game 3
-2.1 inches, Yankee Stadium, Game 4
-1.0 inches, Yankee Stadium, Game 5
 
-5.5 inches, Rangers Ballpark, Game 6

The PITCHf/x system in Philadelphia seems to be the only one that's really well calibrated with regard to plate location.  The system in San Francisco was off about two inches, which is quite a lot.  The system in Yankee Stadium was off about an inch, which isn't great but is more within the realm of normal operation.  But the system in Texas, which wasn't calibrated particularly well in the first two games of the series, went positively haywire in Game 6.  

This is actually the fourth-worst excursion observed at a single-game level in the 2008-2010 time frame.  Some of those were probably statistical flukes from my measurement method, but the strike zone called by the umpire tonight suggests that this was not a statistical fluke.

PITCHf/x plate locations, and thus the television PitchTrax locations, really were off by about 5-6 inches in Friday's Game 6.  Please retract all tomatoes thrown at Brian Gorman on the basis of the PitchTrax data.

EDIT: Corrected the name of the home plate umpire.

Mike Fast is an author of Baseball Prospectus. 
Click here to see Mike's other articles. You can contact Mike by clicking here

11 comments have been left for this article. (Click to hide comments)

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Festsgrber

That does explain how a batter walks when all the
pitches are inside the blue box.

Oct 23, 2010 06:13 AM
rating: 2
 
RedsManRick

It makes me wonder just how much those pitch tracker graphics influence those fo us watching the game. My eyes told me he was giving the guys a ton of room on the outside of the plate for lefties. But given the offset from the cameras, perhaps the graphic was introducing a bias.

I do wonder, why not simply have a camera looking straight down on top of the plate? If not to adjust the calibration the interpretation of data as it comes in to the system in real time, at least to provide a second input on TV?

Oct 23, 2010 09:13 AM
rating: 2
 
BP staff member Mike Fast
BP staff

I'm always happy with more views. However, if PITCHf/x is well calibrated, the PitchTrax graphics should do a very good job of reproducing the pitch trajectories and locations.

In terms of horizontal offset, the PITCHf/x strike zone bias is within half an inch 50% of the time, within one inch 80% of the time, and within two inches 98% of the time.

So to see it this far out of calibration is really surprising.

Oct 23, 2010 12:27 PM
 
Mountainhawk

What would cause it to move 3 inches from game 2 to game 6 in the same park? Is it possible it's really more like 3 inches off, and the 1st game was inaccurate 1 way, and game 6 the other.

Being off almost half a foot is almost inexcusable.

Oct 23, 2010 12:36 PM
rating: 0
 
BP staff member Mike Fast
BP staff

I've notified Sportvision of the problem so they can look into what went wrong. They're the ones with access to the raw data from the cameras that could provide a definitive answer to what happened to the camera. I could speculate what might have happened, but that wouldn't be productive.

The standard deviation on my method for one game is about one inch. So ~68% of the games will be estimated within one inch, and ~95% of the games will be estimated within two inches. It's possible that this game was an outlier at four standard deviations and the umpire was off by five inches on his zone. However, it seems reasonable to me that since the estimate from my method and the zone called by the umpire agree, the PITCHf/x system really was off by 5-6 inches.

Oct 23, 2010 13:14 PM
 
Mountainhawk

What would you attach that camera to? It couldn't be low enough to potentially interfere with a pop up, and you wouldn't want it interfering with any sight lines.

Oct 23, 2010 12:37 PM
rating: 0
 
Richard Bergstrom

Why not do it the other way? Put some kind of technology in home plate like a motion sensor that can track the location of the ball as it flies over it?

Oct 24, 2010 13:39 PM
rating: 0
 
BP staff member Mike Fast
BP staff

Wouldn't any technology you use be subject to problems, just like the PITCHf/x cameras? They do a pretty good job, but there's nothing in this world that's going to be perfect and reliable 100% of the time.

Oct 24, 2010 14:07 PM
 
TangoTiger

Mike, I don't think talking about "perfect is the enemy of the good" is worth bringing up. That's like talking about PED and someone uttering "won't someone think of the children". It's not relevant to the discussion because that's not the point being discussed.

I think what would be helpful for us neophytes is understanding the choices being made by the technologists, and what drawbacks the other considered and discarded systems have. For example, how can we, or not, apply the tennis-line technology? Can we put attach sensors on home plate, presumably making it a fixed point? What kind of miscalibration can we have? Will these help in conjunction with the rest of PITCHf/x? And can Trackman complement, or usurp, PITCHf/x? How about the FoxPuck on a baseball (presumably the baseball is too soft, compared to a puck).

Basically: what are our choices, what do they do, what don't they do, and this is why ultimately they are not helpful.

A followup article would be cool...

Oct 26, 2010 17:02 PM
rating: 0
 
BP staff member Mike Fast
BP staff

Tom, good questions. My response ended up going into a bit more detail than would fit well here, so I added a new blog post for it:
http://www.baseballprospectus.com/article.php?articleid=12325

Oct 26, 2010 21:02 PM
 
TangoTiger

Great, thanks, I appreciate the quickness and thoroughness.

Oct 27, 2010 07:55 AM
rating: 0
 
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