We learn that our Red Stocking club have secured Dennis McGee, the "Mack" of the Philadelphia club last season, now playing with the Lone Stars of New Orleans as their second baseman.
-St. Louis Republican, February 21, 1875
The reason that's important is because I've never come across anything that has explained why the Reds signed Charlie Sweasy for 1875. They had a team full of St. Louis amateurs, except for the veteran Sweasy, who was named the club's field captain. The signing makes sense because the Reds were a young club that had no experience at the top level of baseball and bringing in Sweasy gave them a veteran hand who could help lead the club through the trials of championship, professional baseball. But I've never seen a contemporary explanation for the signing and I've been looking for it for almost a decade.
One of the things I did find about Sweasy was that the Browns almost signed him. So we have the Reds looking for a veteran and Sweasy already open to the idea of signing in St. Louis. Once the Mack signing fell through for the Reds and the Browns decided against signing Sweasy, it's kind of obvious what happened.