Effect of Changing Baseball Parameters

Alan Nathan, March 29, 2021

The table below shows the effect of changing various baseball parameters on exit velocity (EV) and fly ball distance. These numbers were taken from the May 2018 report of the MLB Home Run Committee, Appendices A and B (slightly updated, see link below). Note that increasing the weight by 0.125 oz decreases the EV (resulting in a decrease in distance by 4.6 ft) and decreases the drag acceleration (resulting in an increase in distance by 3.5 ft), so that the net change in distance is a decrease of 1.1 ft. Increasing the circumferences does not affect the EV but increases the drag, thereby reducing the distance. All the effects shown in the table are both linear and uncoupled in their effect on distance for small changes in the parameter. Therefore to see the effect of any small change, simply scale appropriately, make sure the sign is correct (i.e., change the sign if the parameter has decreased), and add.

Note that the “CCOR” is the “Cylindrical Coefficient of Restitution” and is a measure of the “bounciness” of the ball. A higher CCOR means the ball leaves the bat with a higher speed, all other things equal. It is a quantity that can be measured in the laboratory. Rawlings does their own measurements on samples of ball lots on a regular basis. In addition, MLB employs an independent research laboratory to do measurements of CCOR as well as other features of the baseball.

Consider the following made-up example (i.e., these numbers have nothing to do with any actual change in the ball): Suppose the weight is smaller by 0.1 oz, the circumference is smaller by 0.05 in, and the CCOR is smaller by 0.01. The net effect on distance will by:

1.1*(0.1/0.125) + 3.7*(0.05/0.125) -4.9*(0.01/0.008) ft, or -3.8 ft.

Baseball Parameter	MLB specification	change	Change in EV (mph)	Change in Distance (ft)
weight	5.125 ± 0.125 oz	+0.125 oz	-0.94	-4.6 + 3.5 = -1.1
circumference	9.125 ± 0.125 in	+0.125 in	---	-3.7
CCOR	0.4825 ± 0.0225	+0.008	+1.00	+4.9

Reference: Report of the Home Run Committee, May 2018.

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