The police made a descent on Ferguson Hall, on Beadle street [in St. Louis], last night, and captured some twenty persons, mostly boys, on a charge of belonging to the Ku Klux Klan. On the person of one of them was found a document purporting to be a constitution of that order, putting forth that the object of the order was to protect the people of the South from the bands of robbers and murderers now preying on them even to the last resort, assassination, pledging themselves to allow nothing to deter them from their object. Among the captures were a lot of masks and a skull. The boys claimed they were members of the Pride of the South base ball club, and had no connection with the Klan, and knew nothing of the papers found; that it was a plot against them. They were taken to the Southern station house and kept until two o'clock this morning, when they were all unconditionally released.
-New York Herald, April 8, 1868
A quick search shows no record of a St. Louis club playing a club called the Pride of the South in April of 1868 but that doesn't mean much. St. Louis clubs did play several southern clubs during this era, specifically clubs from Louisiana and Arkansas. But obviously, the more interesting thing here is that the club was made up of Klansman and that you could get arrested in St. Louis in 1868 for belonging to that organization.
It wasn't all amateur sportsman and gentlemanly competition back then, was it?