The Two-Hundredths of an Inch That Changed College Baseball
The 2015 NCAA home-run boom was an aerodynamics story; the ball's seam height dropped by seventeen thousandths of an inch.
In 2014, NCAA Division I baseball averaged 0.39 home runs per game — the lowest mark since the BBCOR bat standard came in. Coaches were complaining; television was complaining. The Division I Baseball Committee did one thing about it: they changed the ball.
The new ball, in play for the 2015 championship and then league-wide, had a seam height of .031 inches. The old one was .048. Seventeen thousandths of an inch — less than the thickness of a sheet of cardstock.
Washington State's Sport Science Laboratory had run the numbers in advance. At a launch of 95 mph, 25 degrees, and 1,400 rpm of backspin, the flat-seam ball flew 387 feet on average. The raised-seam ball went 367. The drag coefficient, measured separately, came out about 25 percent lower for the flat-seam version. Lower seams catch less air; less drag means more carry.
The season-by-season jump was almost cartoonish. From 0.39 home runs per game in 2014 to 0.56 in 2015, 0.61 in 2016, and 0.75 in 2017. Across Division I, that 2017 figure was nearly double the pre-change rate.
What the change exposes is how thin the margin is between a flyout and a home run. The hitters didn't get stronger. The pitchers didn't get worse. A rule committee adjusted the stitch by less than two-hundredths of an inch and a generation of college power numbers reorganized themselves around the new aerodynamics.
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