Great point. Those would make for some good postcards. Of course, there are virtually millions of baseball cards out there, and some baseball postcards too. Not in my collection, but here is a cool 1950s Florida postcard showing Clearwater Stadium and the Phillies in spring training:
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Before expansion in 1961, there were 16 teams in two leagues. It's hard to make out the teams playing, and whether any regulars or stars are in the scene. I'm guessing the team in red are the Phillies (but who knows, perhaps it's the Reds, Red Sox, Cardinals, etc).
Not sure when the others moved to AZ for Spring Training, but by the 1950's the Indians, Giants, and Cubs would have already moved there, so that should narrow down which team is playing the Phils in this photo somewhat.
First off, boy, how times have changed! I can't imagine a Spring Training game so sparsely attended in this day and age.
As for the visiting team, it's hard to tell. All we really have to go on is the hat, sleeve and stirrup color. Wandering over to the Hall of Fame's uniform database, depending on the year, it could be the Pirates, Philadelphia Athletics, Yankees, or Tigers. Several dark-hatted and sleeved teams had colorful horizontal stripes on their stirrups, so that narrowed it down quite a bit.