The deadball era.

Paraphrased from "The History of Baseball"

The baseball changed in composition several times during the late 1890s and early 1900s. It did not carry well or take high hops like today's version. This less responsive ball contributed to a style of play that emphasized speed and strategy rather than the home run. It gave its name to the period of baseball between 1901 and 1920: The dead ball era.