The World Series was broadcast on the radio for the first time on this date in 1921.
Before radio, reporters would telegraph World Series information to centers where game boards were set up to display to thousands. The 1921 World Series was broadcast over radio stations in Pittsburgh, PA; Springfield, MA; and Newark, NJ. The Pittsburgh radio coverage was live from the Polo Grounds. Meanwhile, radio signals in the other two cities were relayed, and a sportswriter sent play-by-play reports/summaries via the telephone. The 1922 through 1926 World Series was carried by Westinghouse Broadcasting and were available to any commercially operated radio station. The 1923 World Series was the first true, stadium originated radio broadcast. The 1927 World Series was the first to be broadcast from coast to coast over a full radio network.
As a side note, Westinghouse radio and later television was affiliated with NBC, but later changed to CBS affiliations before buying the network in 1995. (from Wikipedia)