The first baseball game in Olympic history was an demonstration game between host country Australia and the United States on December 1, 1956. There were 114,000 people
in attendance, making it the largest crowd ever to witness a baseball game. This large turnout was not due to international excitement to see our national pastime but was a result of the game being scheduled before that days track and field events.
The game was only six innings and no future stars or legends took part that day as the Australian team consisted of the country's top amateur players and the United States team was comprised of servicemen stationed in Asia as part of the military's Far East Command. The USA won the game 11 to 5 and more details on the game including rosters and the box score can be found here.
The wonderful Ebbets Field Flannels has made some cool reproductions of the USA team's hat and jersey.