St. Louis Maroons/Indianapolis Hoosiers

The St. Louis Maroons debuted on April 20, 1884, at the Union Base Ball Park, defeating Chicago Browns, 7–2.

Henry Lucas, the founder and president of the Union Association and owner of the Maroons, had stocked his team with most of the league's best talent.

The mark has never been surpassed in Major League Baseball, with the closest teams being the 1982 Atlanta Braves, the 1987 Milwaukee Brewers, and the 2023 Tampa Bay Rays (who all started the season 13–0).

For comparison, the Maroons' record would project to 135–27 under the modern schedule of 162 games, while Pythagorean expectation based on the Maroons' results (887 runs scored, 429 runs allowed) and a 162-game schedule would translate to a record of 132–30, but these results are of questionable merit, and serve to indicate something of the quality of the remainder of the organization, which many derided as the "Onion League".

Due to blue laws, the club staged Sunday games outside the city limits, at Bruce Grounds in 1887 and at Indianapolis Park during 1888–89.

Baseball Hall of Fame member Amos Rusie made his big league debut with the 1889 Hoosiers.