THE BOOK--Playing The Percentages In Baseball

Speaking from a highly personal point of view, I am very pleased that scientifically based predictions of a significant reduction in home run production with the new bats is actually realized.

What kinds of predictions were made for offensive levels with the new bats? How close is 1.7% HR/batted ball (or other measures)?

It’s hard to predict precise numbers for home run production.  But here is what we were able to predict.  We estimate that the maximum batted ball speed with the new bats would be reduced by about 5%, or about 5 mph.  For long fly balls, such a reduction will result in a corresponding reduction in distance by about 25-30 ft.  I would say that we know that number quite well. 

To make predictions on home run production using that number requires either lots of data on fly ball distances or some rough estimates.  Lacking the former, let’s try the latter.  In Adair’s book The Physics of Baseball, he estimates for MLB stadiums a 7% reduction in home runs for each 1% reduction in fly ball distance.  That number agrees pretty well with my own analysis that I did for my Baseball ProGuestus humidor article from a month or so ago.  In MLB, the mean home run distance (extrapolated to ground level) is about 400 ft, so a reduction of 30 ft is 7.5%, resulting in about a 50% reduction in home runs, which is not so far off from the actual reduction.  However, I would not want to emphasize that agreement.  Rather I would emphasize that the both the predicted and the actual reductions are huge.

1.7% is about what I would expect for hitters between ages 18-21 if they were using wood bats.

Take the good pitchers and hitters from NCAA div I, after at least 3 years of experience/physical maturity, and give them wood bats.  This is what Pro baseball does each year in the Northwest and NY-Penn leagues.  In 2010, those leagues each had homers on 1.9% of AB-K.

Most college draftees go to these leagues to start.  The very best go to A+ or AA at the end of the summer, but that’s a small percentage of players.

Another alternative is to look at what college players hit in the Cape Cod league.  They play with wood bats there, and from what I recall run scoring is hard to come by.  Even though Ryan Dunne is no longer pitching there.

Alan,

If I use these parameters:

mean flyball distance = 270 feet (presuming it’s low in college)
one standard deviation = 70 feet
min HR threshhold = 360 feet

Then 10% of the flyballs will exceed the threshold.  In other words, the HR threshold is 1.28 standard deviations from the mean, and that implies the 90th percentile.  (360 - 270 divided by 70).

(The non-circular nature of fences makes this exercise a little uncertain, but, it at least gives us something to work with.)

If I use your number, and drop the distance of each batted ball by 7.5%, as well as the SD by the same amount, then 4.5% of the data points would exceed the threshhold.

So, on a quick check like this, I would have said a drop of 55%. 

I agree that we knew it was going to be very substantial, and it was just a matter of how much.

+1 for science and math

Nice work, Tom.  The key to making good estimates is to do it in different ways and with different assumptions and see if you get about the same answer.  So, it’s nice that we did!

An interesting anecdote to this article and conversation:

I watch lots of Northern California high school baseball, and the leagues I watch have all conformed to the same BBCOR guidelines as the colleges (I believe all California high schools will be required to by 2012).

The reduction of power is noticeable at the high school level as well.  But not in a reduction of home runs; those were already scarce.  Instead, what is noticeable is that varsity outfielders seem to be playing at least 15 feet more shallow all the way around.  When you are used to watching the pro game, and then you go out and watch high school, it’s startling to see the entire outfield positioned ~30 feet away from the lip of the infield dirt.

@8/Jacob Jackson

I actually cover Norcal High school sports, and I believe according to this press release (http://cifncs.org/sports/baseball/files/CIF%20Plan%20to%20Tighten%20Bat%20Standard%20release%20(3).pdf) that the proposed adjustments affect this season. Though I’m not sure how many teams are actually implementing them.

For those who don’t know, this was a response to Gunnar Sandberg’s horrifying injury (also shown displaying the “pitching helmet” Tango linked to a while back) in which he suffered a line drive off his head. I haven’t seen enough strong baseball teams to illustrate the effects of the bats yet, so I’m not in a position to comment on it.

15 feet would seem to be about correct.  If they normally play at 165 feet and are now at 150 feet (let’s say), that’s 9% closer, and in keeping with the 7.5% that Alan mentioned.