Alot of times when uniforms from the 1870s are found, that are generic, with no numbers letters, sporting goods label, or insignias anywhere, there may be no way of telling a fireman, or other occupational uniform from a baseball one.
It is obvious in this tintype because of the hook & ladder company number "1" on the belts, but many of the other parts are nearly identical to baseball at that time. These are very common for the inexperienced to think or claim they are baseball players.
