The maximum number of balls a batter can receive before being walked is four. When the umpire calls the fourth pitch outside the strike zone without the batter making a swing that produces a strike, the batter is awarded first base.
This event is officially called a base on balls and is commonly known as a walk. It does not count as a hit or an at-bat, so it does not lower or raise a player’s batting average. However, it counts as a plate appearance and increases the batter’s on-base percentage.
The rule has not always required four balls. Baseball’s walk threshold changed repeatedly during the nineteenth century: different rule sets used totals such as nine, eight, seven, six, and five. The modern four-ball standard was adopted by the National League and American Association in 1889.
A hit-by-pitch is different from a walk even though it also awards first base. In a hit-by-pitch, the batter is struck by the pitch; in a walk, four called balls accumulate.