Any ideas on this postcard?

[Laxcat]

I was digging through storage, getting ready for the Plano Show, and found this postcard. It looks like football to me. Yall have any guesses on how old or subject?

[Laxcat]

.

[FourStrikes]

AZO 4 triangles up stamp block: 1904-1918...divided back = 1907 and later, so issued 1907-1918.

source: http://www.playle.com/realphoto/

IMO, yes, it's football.