As the game progressed towards professionals and became more serious, pitchers began to attempt to prevent the batter from hitting the ball by throwing faster pitches. With the introduction of the called strike in , catchers began inching closer to home plate due to the rules requirement that a strikeout could only be completed by a catch. The rules governing the delivery of pitches proved to be hard to enforce, and pitchers continued to stretch the boundaries of the rules until the 1870s when the release point of pitches had reached the pitcher's waist level. Pitchers had begun throwing overhand by , when, the National League made a rule change removing all restrictions on the pitcher's delivery.