A baseball is a ball used in the sport of the same name. The ball features a rubber or cork center, wrapped in yarn, and covered, in the words of the Official Baseball Rules "with two strips of white horsehide or cowhide, tightly stitched together." It is 9–91⁄4 inches (229–235 mm) in circumference (2 55⁄64–2 15⁄16 in. or 73–75 mm in diameter), with a mass of 5 to 51⁄4 oz. (142 to 149 g). The yarn or string used to wrap the baseball can be up to one mile (1.6 km) in length. Some are wrapped in a plastic-like covering.
A significant quality of the baseball is the stitching that holds together the covering of the ball. After a ball has been pitched, these raised stitches catch the air and cause the ball to swerve slightly on its way to the catcher. Whether the ball swerves to the right, to the left, downward, or a combination thereof, and whether it swerves sharply or gradually, depends on which direction, and how fast, the stitches have been made to spin by the pitcher. See, for example, curveball, slider, two-seam fastball, four-seam fastball, sinker, cutter.
Cushioned wood cores were patented in the late 19th century by sports equipment manufacturer Spalding, the company founded by former baseball star A.G. Spalding. In recent years, various synthetic materials have been used to create baseballs; however, they are generally considered lower quality, stiched with two red thick thread, and are not used in the major leagues. Using different types of materials affects the performance of the baseball. Generally a tighter-wound baseball will leave the bat faster, and fly farther. Since the baseballs used today are wound tighter than in previous years, notably the dead-ball era that prevailed through 1920, people often say that the ball is "juiced". The height of the seams also affects how well a pitcher can pitch. Generally, in Little League through college leagues, the seams are markedly higher than balls used in professional leagues.
In the early years of the sport, only one ball was typically used in each game, unless it was too damaged to be usable; balls hit into the stands were retrieved by team employees in order to be put back in play, as is still done today in most other sports. Over the course of a game, a typical ball would become discolored due to dirt, and often tobacco juice and other materials applied by players; damage would also occur, causing slight rips and seam bursts. This would lower the offense during the games giving pitchers an advantage. However, after the 1920 death of batter Ray Chapman after being hit in the head by a pitch, perhaps due to his difficulty in seeing the ball during twilight, an effort was made to replace dirty or worn baseballs.
In 1909, sports magnate and former player Alfred J. Reach patented the ivory centered "ivory nut" in Panama and suggested it might be even better in a baseball than cork. However, Philadelphia Athletics president Benjamin F. Shibe, who had invented and patented  the cork centered ball, commented, "I look for the leagues to adopt an 'ivory nut' baseball just as soon as they adopt a ferro-concrete bat and a base studded with steel spikes." Both leagues adopted Shibe's cork-centered ball in 1910.
The official major league ball is made by Rawlings, which produces the stitched balls in Costa Rica. Attempts to automate the manufacturing process were never entirely successful, leading to the continued use of hand-made balls. The raw materials are imported from the United States, assembled into baseballs and shipped back.
Throughout the 20th Century, Major League Baseball used two technically identical but differently marked balls. The American League had "Official American League" and the American League's president's signature in blue ink, while National League baseballs had "Official National League" and the National League president's signature in black ink. According to Bob Feller, in the 1930s, when he was a rookie in the National League, baseball laces were black, intertwined with red; the American League's were blue and red. In 2000, Major League Baseball reorganized its structure to eliminate the position of league presidents, and switched to one ball specification for both leagues. Under the current rules, a major league baseball weighs between 5 and 5 1⁄4 ounces (142 and 149 g), and is 9 to 9 1⁄4 inches (229–235 mm) in circumference (2 7⁄8–3 in or 73–76 mm in diameter). There are 108 double stitches on a baseball, or 216 individual stitches.
Today, several dozen baseballs are used in a typical professional game, due to scratches, discoloration, and undesirable texture that can occur during the game. Balls hit out of the park for momentous occasions (record setting, or for personal reasons) are often requested to be returned by the fan who catches it, or donated freely by the fan. Usually, the player will give the fan an autographed bat and/or other autographed items in exchange for the special ball.
Balls used in the professional game are rubbed with a mud known as "rubbing mud", which is typically applied by the umpire before each game, and is intended to help the pitcher's grip.
There are different types of baseball used.
- Baseball or Hard baseball – Ordinary baseball which is used in Major League Baseball, in Japan is used in high school baseball and above for (hardball) baseball, referred to as hardball or baseball
- Rubber baseball aka Nanshiki – Used for rubberball baseball usually played prior to high school in Japan; sometimes referred to as Japanese rubber baseball
- Soft (compression) baseball – Used for batting practice and fielding training or softball baseball which can be safely played indoors, usually made from polyurethane (PU) material