The First Game of Modern Baseball

The first game of baseball played under the Knickerbocker Rules, the set of rules that form the foundation of modern baseball, was played in Hoboken, New Jersey on June 19, 1846. The New York Nine defeated the New York Knickerbocker Base Ball Club 23 to 1 in four innings on the Elysian Fields, a resort area on the Hudson River. The Knickerbocker Rules, written by club member Alexander Cartwright, introduced the concept of three strikes and the diamond-shaped infield, among other fundamentals still in use today.

Source: Wikipedia