Major League Baseball outlawed the extremely effective spitball in 1920. Hitters have a more difficult time seeing dirty baseballs, as opposed to new ones. Dirty baseballs move unnaturally and erratically, rendering them more difficult to hit. Baseballs soften with continued use, and it is more difficult to hit home runs with soft baseballs.
The dead-ball era of baseball occurred between 1900 and 1919. Baseball historians refer to the period as the dead-ball era due to a decrease in scoring and lack of home runs. In the 1920 season, Ray Chapman died after getting hit in the head with a dirty baseball while batting. In response, Major League Baseball required that more baseballs be used per game. Scoring increased dramatically as a result of more baseballs being used per game, ending the dead-ball era.
Which one of the following statements, if true, most weakens the argument?