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The Complete Handbook of Baseballs
A Professional's Guide to Selection, Use, and Care of Baseballs for Teams, Leagues, Facilities, and Serious Players
by Alumigogo Books
Chapter 1: Understanding Baseballs
A baseball is a deceptively simple object. Externally, it is a sphere of leather held together by stitching, weighing between 5 and 5.25 ounces, with a circumference of 9 to 9.25 inches. Internally, it is a composite of materials engineered to perform under violent, repeated impact. To treat a baseball as an interchangeable commodity is to misunderstand the product you are buying. The difference between a professional-grade ball and a training ball is not merely marketing; it is a difference in materials, construction tolerances, and performance characteristics that have measurable effects on the game.
Understanding what a baseball actually is starts with understanding its core. The core is the heart of the ball and the primary determinant of its weight, firmness, and "liveliness." Historically, cores were made of rubber or cork. Today, the vast majority of baseballs use a core made of a combination of cork and rubber. The specific blend and the way the core is manufactured influence the ball's Coefficient of Restitution (COR), which is a measure of how much energy is returned when two objects collide.
Think of COR as the efficiency of a bounce. If a ball is dropped from a fixed height onto a solid surface, a ball with a higher COR will bounce back closer to its original drop height. For baseballs, the standard test involves firing a ball at a wooden wall at a specific speed and measuring the rebound speed. The COR is the ratio of rebound speed