Softball COR and Compression

Softballs are rated based on two metrics - Coefficient Of Restitution (COR - pronounced like core) and compression. COR represents how "bouncy" the ball is. The higher the COR, the more bouncy the ball is and, generally, the farther it will fly. COR is the percentage of reduction in speed for a ball bouncing off a wall. If a ball is thrown at a wall at 80 miles per hour and bounces off at 40 miles per hour, the speed has been reduced by 50%. The ball would be rated with a COR of .50 (referred to as a fifty COR ball). If your league plays with a .44 COR ball, the speed bouncing off the wall would be 35 miles per hour.

Softball compression is a measure of how hard a softball is. The higher the compression, the harder the ball, and generally, the farther it will fly. Compression is measured by how many pounds of force are needed to squeeze two sides of the ball in by a total of one-quarter of an inch. If a test shows that it takes 375 pounds of force to squeeze the ball by one-quarter inch, the ball is certified as a 375 pound compression ball. The ASA has only approved two levels of compression - 375 pounds and 525 pounds. 375 pound balls are softer than 525's. The ASA "rounds up" to assign the compression rating. For example, if the test shows it only takes 325 pounds of force to achieve the one-quarter inch squeeze, the ball will be rated as a 375 compression ball. This means your league may be playing with a ball rated as 375 compression, but it is really softer than a true 375 compression ball because of the "rounding up."

Testing has shown two main things as it relates to softball COR and compression and on-field performance. First, a change from a .47 COR, 525 pound ball to a .44 COR, 375 pound ball decreases performance by up to 6%. All other things being equal, this means that a 305 foot home run using a .47 COR, 525 pound ball would be a 290 foot fly out using a .44 COR, 375 pound ball. Second, reductions in compression have a much greater impact in on-field performance than reductions in COR.

As a player, you should also be aware that weather has an enormous impact on the compression of a softball. Studies have shown that when the temperature is 100 degrees, an average softball looses 200 pounds of compression as compared with the same softball at 60 degrees. This means that a softball that is a 525 pound compression ball at 60 degrees may play like a 375 pound ball at 100 degrees. In addition, clouds, rain, and humidity also affect the compression of a ball. 70 degrees and sunny creates lower compression balls than if it was 70 degrees and cloudy. Leather balls generally take on more moisture in rainy or humid conditions than synthetic balls. This will generally raise the compression and level of play up to a point, then performance will decline once the ball takes on too much water and becomes too heavy.

Keep these factors in mind when deciding which bat to use and when determining your approach for each at-bat. If it is hot and humid, it may be best not to try for a home run, but instead try for a base hit.