Now the estimable Tom Tango has added some support for that viewpoint, at least with regards to parks and expansion. Comparing matched sets of head-to-head plate appearances between hitters and pitchers in the same park against all other pitcher/hitter/park combinations, Tango found virtually identical changes in home run frequency (HR per contact PA) from 1987 to 1988, and from 1992 to 1994. That is, both the matching combo and the unmatched combo saw their homer frequencies change at comparable rates during the same periods, first from 1987 to 1988, when a one-year home run spike came and went, and then from 1992 to 1994, a span in which homer and scoring rates escalated to levels that would be common over the next decade.Like me, Tango then turned his attention to the baseball itself as an engine for the rise in home runs, and to evidence found via the University of Massachusetts-Lowell's series of tests back in 2000. But it appears he was a little off base when he tried to connect the ball's compositional changes with some data pertaining to fly ball distances:
In Tango's piece, he turns his attention to the ball as well, and to the UMass-Lowell testing in particular, focusing on testing director Dr. James Sherwood's report of an 8.7-foot difference in flight distance between tested major league balls and minor league ones, which differ in the compositions of their cores. Extrapolating from data provided by Greg Rybarcyzk of HitTracker Online, Tango finds that, lo and behold, an 8.7-foot decrease would reduce home run rates to almost exactly where they were in the decade prior to the surge. A tidy little explanation for where those extra long balls might have come from, right?Take a picture, kids -- it's not often a hack like me can legitimately find fault with the work of one of the field's top researchers. Then again, Enrique Wilson did get a few hits off Pedro Martinez, and D.J Houlton has struck out Albert Pujols in their only two encounters. It happens.
Not quite. Tango implies that what took place may have been as simple as MLB and Rawlings, the ball's current manufacturer, replacing balls made with a pure cork center (as specified for the minor league balls) with ones made with a compressed-cork center (a composite of cork and ground rubber, known as cushion cork or cushioned cork, which is part of MLB's official specifications for the ball). In actuality, the cushioned cork center ball is decades old: according to information provided by the Spalding company (which manufactured the balls up through 1976), it was officially adopted in the major leagues way back in 1926. Oddly enough, the words "cushioned cork center" imprinted on MLB balls were removed in 1999, the year before the UMass report was published, although the report notes that rubber continues to be added to the pill, the innermost element of the ball...
Though rubber and cork are still in the pill, its exact composition appears to have changed over the past couple of decades. A team from Universal Medical Systems confirmed this last summer, when they compared computerized tomography (CT) scans of baseballs from different eras. Whether simply due to technological advances incorporated into the manufacturing process or a calculated desire to produce more home runs, the pill has increased in size and density over the years. And that's without considering the aforementioned synthetic ring, or the increasingly synthetic composition of the yarn used to wind the ball, something a University of Rhode Island study identified back in 2000. While Sherwood and company continue to test balls on an annual basis for MLB and have even shown some teeth by criticizing the outdated specifications of the testing, they've remained conspicuously quiet as to the impact of the composition changes, to say nothing of MLB bulldozing its own published specifications.
Since this article's publication, several readers have pointed out that while the fair territory of playing fields aren't getting smaller, a decreasing amount of foul territory may be contributing to the rise in homers and scoring in general. That's something I'll be examining in my next take on this subject.MLB 1990 2007 ChangeWith the exception of the teensiest of fractions for straightaway center field, fence distances have actually increased during the wave of building that's put 21 clubs (including four expansion teams) into new ballparks. What has decreased during the time period in question -- indeed, what may be confusing the issue -- is smaller park capacities. In 1990, the average ballpark held 53,057 patrons; last year it was 48,219, a drop of about 10 percent. So yes, parks are smaller, but not in a way that carries any ramifications for home run levels.
LF 329.6 332.0 2.4
LCF 375.5 376.6 1.2
CF 404.9 404.9 -0.1
RCF 376.0 377.6 1.6
RF 329.1 329.3 0.2
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