THE BOOK--Playing The Percentages In Baseball

And here are comments from two Primer readers.  Based on the links provided in the comments from pobguy, and the name used by gator (identical to the one in SOSH and at Fever), we can guess who those two guys are:

20. pobguy Posted: June 30, 2009 at 11:22 AM (#3237688)
Some comments from a physicist who has done extensive work in the physics of baseball:

1. The authors purport to calculate the “energy expended” by the ball in flight. What exactly is meant by that? Is it the initial energy minus the final energy? And what is the relevance of this quantity? I simply do not know how to interpret the “Weight” numbers in Table 2.

2. The discussion about the forces on a baseball (Fig. 2) is wrong. The “wind” is not an additional force. Rather, the wind affects the speed of the baseball with respect to the air The statement that the air drag is opposite to the velocity is correct. However the velocity in that case is the velocity of the ball with respect to the air, not with respect to the ground. It is that relative velocity that affects both the drag and the Magnus forces. It would appear that the authors did not take into account the affect of wind on the Magnus force. Finally, the estimate of Adair in his book of the Magnus force is almost surely wrong and underestimates the effect of spin on the flight of a baseball by a lot. For a dicussion, see http://webusers.npl.illinois.edu/~a-nathan/pob/AJPFeb08.pdf.

3. The results regarding the optimum launch angle cannot possible be right. There is no way that the optimum launch angle is greater than 40 degrees. An inspection of home run data from hittrackeronline.com shows that very few home runs are hit with a launch angle that steep.

4. The assumption about the magnitude of the backspin is probably not right, as it is well-known that the backspin is a function of the launch angle. Generally, the larger the launch angle, the larger the backspin.

5. The commment about the ball-bat contact time being 0.005 sec is not even close. It is more like 0.001 sec.

6. If the authors want to contact me privately at my e-mail address, I would be happy to carry on a dialogue with them about baseball aerodynamics.

21. pobguy Posted: June 30, 2009 at 02:30 PM (#3237947)
One more comment that I forgot in the previous post:

7. The spin-down time constant of 5 seconds that Adair has in his book is also probably not correct. The time constant is much longer, probably more like 25 seconds, an number based on actual (albeit a bit crude) data as well as scaling from careful measurements on golf balls. See http://webusers.npl.illinois.edu/~a-nathan/pob/spindown.pdf

8. I think I finally figured out what the “energy expended” is. If I am not mistaken, it corresponds to the minimum velocity needed for the ball to clear the fence. The idea for the calculation is a good one. The work could be improved with a better aerodynamics model.

22. gator92 Posted: June 30, 2009 at 09:58 PM (#3238468)
Maybe I shouldn’t pile on, but a lot of the fence heights are wrong as well.

- There aren’t any 11 foot fences in AT&T;Park in LCF (nor anywhere in the park)
- The LF fence at Dolphin Stadium (Land Shark now) is considerably less than 33 feet.
- The Mets fences listed are incorrect whether they are intended to represent Shea Stadium or Citi Field.
- There aren’t any 4 foot high fences in San Diego
- The Angels RCF fence should be 18, and the RF fence less than that (it varies a bit, which is why using only 5 heights is a bad idea)
- CF at Fenway Park is not 9 feet, except for a tiny section where the fence goes from the back left corner of the home bullpen to the front left corner of the bullpen. Silly to use that number for all of CF there.
- The Metrodome LF fence is not 13 feet high. Perhaps when the plexiglass was up, but that was removed quite some time ago…
- The fence heights for new Yankee Stadium are all 8 feet, not the variety of numbers listed. There isn’t a 14 foot fence anywhere in the new or old Yankee Stadium, although you might have been able to find one back before the renovation in the early 70’s.

Seriously, I’ll echo pobguy above and suggest that the authors have made some fundamental, and avoidable, mistakes here.

23. Jeff K. Posted: July 03, 2009 at 07:05 PM (#3241655)
#21/22, I’m not really a physics guy, oddly not really exposed all that much but I can do 90% of the math behind it. So I’m likely the most dangerous guy, the one who thinks he knows more than he does, but your question about what energy expended means (and your followup possible answer), I thought was explained in the second paragraph:

Such an estimate is obtained by calculating1 the minimum energy required to hit a mid-July home run in the different ballparks under a set of reasonably typical conditions for each ballpark. More specifically, the minimum energy for each ballpark is determined for home runs hit down the foul lines, the power alleys, and to dead center.

Am I confusing two different things here?

24. pobguy Posted: July 03, 2009 at 11:45 PM (#3241943)
Re Jeff K. #23: Well, I thought I had figured out what was referred to as “energy expended” but I was wrong. I thought it was the initial kinetic energy of the ball just after leaving the bat. From the table, I take a typical “weight” as 230 lb, which means the energy is the amount of energy need to lift a weight of 230 lb. to a height of 30” (according to the text). If I equate that energy to the kinetic energy of the ball, I find the speed of the ball is about 230 mph! Clearly that is an absurd result, so that means I don’t know what is meant by “energy expended.” Without knowing what that is, it is hard to evaluate what was actually calculated in the paper. The authors of the paper don’t seem to want to respond to any of my posts, even privately, so I guess it will remain a mystery. And aside from that difficulty, there are serious errors in the aerodynamics calculations, as I already noted in #20,21 and as gator92 confirms in #22.

26. pobguy Posted: July 04, 2009 at 12:38 PM (#3242083)
There is another way to approach the issue of home run park factors. Namely, use hitf/x data to find the initial speed off bat (SOB) for every home run, then sort by parks. I have done such an analysis. Since I don’t know how to post an image to this site, I’ll just give a link to the image:
http://webusers.npl.illinois.edu/~a-nathan/pob/v0_by_park.gif.
For each park, the bar graphs shows the mean SOB for all home runs hit there during the first 6 weeks of the 2009 season. A total of 819 home runs make up the data base, so there are roughly 27 per park. Not great statistics but it is the best we can do for now. We will do much better with a full season of data. The error bar shows the standard error on the mean. Coors and Fenway have the lowest mean SOB (about 98.8 mph) while Turner and Chase have the highest (102.8 mph). That’s a difference of 4 mph between lowest and highest, which is a 4% spread in SOB, corresponding to an 8% spread in “initial energy” of the ball.

FYI: hitf/x is the latest from Sportvision, the company that does the technology for pitchf/x. The same camera images that are analyzed to determine the pitched ball trajectory can also be analyzed to determine the initial part of the batted ball trajectory. In particular, the initial SOB and the launch and spray angles are determined.

Another problem is possibly wind direction if they used retrosheet data.

There has been no wind blowing in from right field recorded since 2003.  Not statistically possible and I am wondering if anyone knows if it has been fixed.

Where did they get their elevations?  Safeco Field is nowhere near 429 feet above sea level.  The ocean is barely 429 feet away, and it’s flat between it and the stadium.

I’d say that the most interesting result of this study is the groundbreaking news that the mile-high city is now 5883’ high.

They also seem to have zeroed out the wind in the domed stadiums (retractable and not), but then used the average OUTDOOR temperatures for those cities (e.g. 82 degrees in St. Petersburg, FL, 93 degrees in Phoenix, AZ).

Remember the line in Apollo 13 when Gene Kranz (Ed Harris’ character), amidst a cacophony of damage reports, asks “What have we got on the spacecraft that is good?”