The live-ball era, also referred to as the lively ball era, is the period in Major League Baseball beginning in 1920, following the dead-ball era. During that year offensive statistics rose dramatically in what would be mistakenly attributed to the introduction of a new "lively" ball. While cork-centered balls had been introduced around 1910 (and proved very hitter-friendly), the construction of the balls remained consistent between the transition from the "dead-" to "live-ball eras." More important, several rule changes gave more advantages to the batter.
Before that time, the same ball would be used throughout the game and foul balls would be thrown back on the field and reused. The ball would only be replaced if it started to unravel. As games progressed, the ball would become increasingly dirty and worn, making it difficult to see and its movement erratic. Pitchers were able to help this process along by scuffing it, spitting on it and, since Russ Ford's discovery in 1913, cutting into it with an emery board. The spitball was widely used as well. These factors gave the pitcher a major advantage. The physical wear on the ball from being repeatedly hit also made it less elastic as the game progressed, making it increasingly difficult to hit for distance.
There were also rule changes that contributed to the low-scoring games. In 1901, the National League adopted the "foul-strike rule," which counted foul balls as strikes. Before this rule, batters could safely swing at many marginal pitches, which not only tired out the pitcher but also allowed for more hits because a "flukey" hit could land in play. With the introduction of the foul-strike rule, the batter had to let many more pitches "go" without being swung on, dramatically reducing the total number of hits. The American League followed suit in 1903, making the rule universal.
The dead-ball era came to an end after the fatal beaning of Ray Chapman during the 1920 season. Chapman was killed by a submarine pitch from Carl Mays in the 5th inning of a twilight game. Witnesses stated that Chapman never moved to get out of the way of the ball, and it is assumed he simply couldn't see it. The new Commissioner of Baseball, Kenesaw Mountain Landis, instituted several new rules during that season, both in response to Chapman's death as well as an effort to liven up the game. Starting in 1920, balls were replaced at the first sign of wear, resulting in a ball that was much brighter and easier for a hitter to see. The other major rule change was the elimination of the spitball. The lively ball era was the era in which baseball regained relevance and exploded in popularity.