[rickalaska]

The Philadelphia A's donned a horizontal striped "pill box" cap somewhat similar to these from 1909 through 1914. They became popular throughout the country as the club won four American League pennants and three World Series championships during the six years the cap was worn.

The catcher's glove shown - that pillow style mitt was first developed by JF Draper in 1899 and used up until the 1920s. The guy at the bottom right appears to have a 1910-15 Reach baseman's mitt

The pants don't appear to be quilted

I don't see any "notable" players from this Athletic Club

As indicated by the AZO marking, I would guess the RPPC was from around 1910