Runners? Beautiful Antique RPPC of A Bit of a Motley Group of Young Men

I presume the young men with handwritten numbers pinned to their chest here are runners, but I might guess what connects the somewhat mottly looking group as a whole is something else. Whatever the case, I love the mix of faces and postures and outfits here, and find the image very tender feeling and quite beautiful. Found in Pennsylvania, c. 1910s-20s I believe. 

5 7/16 x 3 3/8". Small burn mark lower left corner and a bit to lower right corner too. Unused postcard back.