The American League was formed in 1901 as a reorganization of the Western League, under its new president Ban Johnson, adding some of the dropped cities while directly challenging the National League in other cities. They opened a new Oriole Park (retroactively called Oriole Park IV, as well as being dubbed American League Park by the contemporary media). It was on the same site but slightly farther north as the 1889–91 field site (located at 39°19′22″N 76°36′37″W) from the last years of the old American Association.

The American League's new Orioles and charter member team played for two seasons before they were transferred north for the 1903 season to become the New York Highlanders (or the New York Americans), as part of a peace pact and recognition agreement between the two competing baseball leagues, and to give the American League a foothold in the nation's largest city. That Highlanders team soon became known as the New York Yankees. Baltimore revived professional baseball as a minor league club, an entry in the Eastern League (later renamed International League), which began play at this same Oriole Park/American League Park. There they were very successful, producing some remarkable and marketable players, including the local star Babe Ruth, who was sold to the Boston Red Sox as a pitcher, and later gained even greater fame as a home run slugger with that same New York Yankees franchise which had begun in Baltimore.

The block was rectangular, with home plate in the northwest corner. A Baltimore Sun piece about the new Terrapin Park on May 29, 1914, gave the dimensions of Oriole Park (IV) as left field 322 feet (98 m), center field 475 feet (145 m), right field 318 feet (97 m).

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