In baseball, the infield is the area inside the diamond, including the bases and the dirt around them, where four defensive players position themselves: the first baseman, second baseman, shortstop, and third baseman. These four players, called infielders, stand ready to field ground balls, catch line drives, and make quick throws to get runners out.

The infield is where much of the fast action happens. When a batter hits a grounder, an infielder scoops it up and fires it to first base, often with only seconds to spare. Infielders need quick reflexes and strong, accurate arms because plays at their positions happen in a flash. A sharp ground ball might reach an infielder in less than two seconds, giving them almost no time to react.

The word contrasts with the outfield, the grassy area beyond the infield where three other players patrol for fly balls and long hits. While outfielders have more ground to cover and need to judge high fly balls, infielders face rapid-fire plays that require split-second decisions. A single game might see dozens of balls hit into the infield, making these positions crucial for preventing runs.