A baseball glove or mitt is a large leather glove worn by baseball players of the defending team, which assists players in catching and fielding balls hit by a batter or thrown by a teammate.
By convention, the glove is described by the handedness of the intended wearer, rather than the hand on which the glove is worn: a glove that fits on the left hand—used by a right-handed thrower—is called a right-handed (RH) or "right-hand throw" (RHT) glove. Conversely, a left-handed glove (LH or LHT) is worn on the right hand, allowing the player to throw the ball with the left hand.
Baseball gloves are measured by starting at the top of the index finger of the glove and measuring down the finger, along the inside of the pocket and then out to the heel of the glove. Gloves typically range in size from 9 inches (youth starter size) to 12.75 inches for adult outfield play. Catcher's mitts, unlike those of other gloves, are measured around the circumference, and they typically have 32- to 34-inch patterns.
The shape and size of a glove is described by its pattern. Modern gloves have become quite specialized, with position-specific patterns:
- Catcher's mitts are called "mitts" because they lack individual fingers, like mittens. They have extra padding and a hinged, claw-like shape that helps them funnel fastballs into the pocket and provide a good target for pitchers. Some catchers use mitts with phosphorescent paint around the ridges to provide a clearer target for the pitcher. In addition, catcher's mitts come in single hinge and dual hinge varieties. If required to catch a knuckleball, a catcher will typically use an even larger mitt. Some knuckleball catchers have even experimented with using first baseman's mitts, as described below.
- First baseman's mitts also lack individual fingers. They are generally very long and wide to help them pick or scoop badly thrown balls from infielders. These mitts usually have 12.5- to 12.75-inch patterns, measured from wrist to the tip. Because first basemen are often left-handed, first basemen's mitts are readily available to fit on a right hand. Hank Greenberg is often credited as the first to wear this style of glove in the field. Some catchers, such as Victor Martinez, use a first base mitt while catching knuckleballers. The disadvantage of using a first baseman's mitt in this way is that because first basemen are rarely required to make a quick throw to another base, they tend to make the task of catching base stealers more difficult—a task already complicated by the knuckleball's slow speed and erratic behavior.
- Infielders' gloves, unlike the first baseman's mitt, tend to be smaller. They have shallow pockets to allow fielders to remove the ball easily in order to make a quick throw to a base. Often the webbing will be open to allow dirt to move through the glove so that the infielder does not pull out a handful of dirt when trying to remove the ball from the glove. Infielder's gloves typically have 11- to 12-inch patterns.
- Pitchers' gloves usually have a closed, opaque webbing to allow pitchers to conceal their grip on the ball (which, in part, determines the behavior of the pitch in flight) from the batter. Pitcher-specific gloves tend to have 11.75- to 12-inch patterns; some pitchers such as Gio González use gloves with patterns as large as 12.25 inches. Infield gloves with intricate webbing are also used by pitchers.
- Outfielder's gloves are usually quite long with deep pockets to help with catching fly balls on the run or in a dive and to keep outfielders from having to bend down as far to field a ground ball. These gloves typically have 12- to 12.75-inch patterns, measured from wrist to the tip. They are frequently worn-in differently from those of infielders, with a flatter squeeze rather than the infielder's rounded style.
- Switch-thrower's gloves are gloves with a second thumb pocket on the opposite side of the glove, to allow it to be worn on either side of the hand. At the major league level, this glove has been used only by switch-pitcher Pat Venditte.
- Left-hand throw gloves are any of the gloves above, but designed to be worn on the right hand (for left-handed players). Players that utilize the left-hand throw gloves such as Tony Gwynn or Sandy Koufax are most frequently pitchers, first basemen, or outfielders.