Been looking at this postcard for a few days for ways to identify it. Probably impossible, but....

.... the uniform letters are strange, the L on the sleeve looks like a place for numbers like the 1912 Oakland Oaks uniforms, so I dismissed it as that. In the close up photo of the uniform with the letters on the chest, "AC", the letters A and C seemed spaced far apart. But in the close up of the image; I think I can make out the outline of a "B", that may have been torn off by a head-first slide, but not re-sewn. If so, ABC, the Atlanta Black Crackers, makes sense. Maybe I'm delusional.