Baseball’s growth spurt, visualized

baseball notes

Baseball is a sport that is susceptible to, and, indeed, has subjected itself to what most regard as extremely fine-grain analysis. For example, in just a few clicks, you can pull up the spin rate of the ball on any pitch thrown in any MLB game last night. Whether we’re examining something, like baseball, for which we have relatively precise analytical tools, or something our ability to probe is more limited, we necessarily operate with certain assumptions practically taken for granted. Gravity. Air. Taxes. The general inflation of the value of U.S. currency over time. The general improvement in human health over time. While we need to monitor these somewhat ambient, environmental facts and trends, it usually doesn’t make sense to address them with great frequency and detail. We all generally know that Al Kaline’s $35,000 rookie signing bonus probably was a lot of money in the 1950s even if it doesn’t sound like a lot by today’s standards, just like we generally know 6’2″, 215 lb. Babe Ruth probably was a lot bigger than his peers, even if he wouldn’t appear out of the physical ordinary today.

On this last point, of course, we’re aware that medical and nutritional advances have resulted in general improvements in human health. Humans today live longer and grow larger than they did in the past, and baseball players are no exception.

That growth hasn’t occurred at a steady rate, however, at least as far as the population of baseball-playing humans is concerned. Here’s a graph from Russell Carleton’s article yesterday at Baseball Prospectus showing the median (50th percentile), 70th percentile, and 90th percentile Body-Mass Index (BMI) of all players who appeared in the majors between 1900-2016:


As Carleton remarks:

We see that in the mid-90s, something (*cough*something*cough*) happened that caused an inflection point in MLB. After most of a century of the same body types, players started getting bigger. Mostly, they got heavier, although players today are also taller than they had been. The median player in MLB right now would be larger (in terms of BMI) than 90 percent of players who played in any year before the 1990s.


For good measure, here’s one more historical-trend graph from that article (which is full of them), showing the percent of MLB players appearing in each season who were born outside of the United States:



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