Despite its uncomplicated appearance, the baseball is in fact a precision-made object, and one that has often been the subject of heated controversy throughout its history.
An official Major League baseball consists of a round cushioned cork center called a “pill,” wrapped tightly in windings of wool and polyester/cotton yarn, and covered by stitched cowhide. Approximately 600,000 baseballs are used by all Major League teams combined during the course of a season. The average baseball remains in play for only 5-7 pitches in a Major League game. Each ball must weigh between 5 and 5.25 ounces and measure between 9 and 9.25 inches in circumference to conform to Major League standards. Your students will enjoy this 5 minute video showing the manufacturing process.
Such uniformity was nonexistent in the early years of baseball’s history, when balls were either homemade or produced on a custom-order basis as a sideline by cobblers, tanners and other small business owners. In 1872, the modern standard for the baseball’s weight and size was established. The production of balls became more consistent during the remainder of the decade, thanks largely to the demands made on manufacturers by the newly formed National League, the first professional baseball league.
At the turn of the century, the baseball had a round rubber core. This gave way in 1910 to the livelier cork-centered ball, which was itself replaced two decades later by the even more resilient cushioned cork model. The baseball has undergone only one significant change since that time, when a shortage in the supply of horses in 1974 prompted a switch from horsehide to cowhide covers.