Just a couple of trivial points (and even more trivial conjecture) for clarification:
Even allowing for considerable inaccuracy and artistic license, the painting and print shown in posts 1 and 9 are surely meant
to depict not the Capitoline Grounds but indeed the Union Grounds, famous for the large three-story pagoda in center field.
We'd also suggest the player shown wearing the A is intended to represent a member of not the Athletics of Philadelphia
but rather of the Atlantics of Brooklyn. The Atlantics and Cincinnati Red Stockings met in 1870 in what was described
as the greatest game ever played.
From the well-researched
http://www.brooklynballparks.com/ :
"The Union Grounds, formally known as the Union Base Ball and Cricket Grounds, were... bounded by Harrison Avenue,
Rutledge Street, Lynch Street, and Marcy Avenue.... the grounds [ were converted ] for baseball for the summer of 1862....
The Union Grounds were demolished in July 1883.
"The Capitoline Base Ball Grounds were conceived in 1863 as a rival to the immediately successful Union Grounds of a year earlier....
In April of that year, the proprieters... offered the powerful Atlantic Club a free lease at their new park.... The Capitoline grounds
stood in Bedford, in a block bounded by Halsey Street, and Marcy, Putnam and Nostrand Avenues.... The only season of major league
baseball at the Capitoline Grounds was in 1872. The Atlantic Club, then of the National Association, won the final major league game there...
but left for the Union Grounds in 1873.... In 1880 the Capitoline Grounds were demolished.
"The finest moment of the Capitoline Grounds was the visit of the awesome Cininnati Red Stockings on June 14, 1870...
Harry Wright's club carried in an 89-game win streak, but suffered a stunning defeat, 8 to 7 at the hands of Bob Ferguson's
Atlantics in 11 innings. This was regarded at the time as the greatest game of baseball ever played, and may still be so."