Ya, It would appear to be c. 1870's fireman and not a ballplayer, particularly due to the "1" on the belt.
I'd suspect it was not originally married to that case either (you're probably already aware of that since you're familiar with tintypes but I'll go on anyway).
Cased tintypes went out of fasion, for the most part, in the mid 1860's. The photographers found they could sell a lot more photographs if they didn't include the expense of a case, so, bye-bye went the case. When you run across a tintype in it's original case you can then pretty much expect that it's late 1850's to mid 1860's (earlier than that time period you were dealing with ambrotypes and daguerreotypes). Had it been original to the case, you'd expect to see no damage to the tintype (bends, etc.) and a much plainer backdrop (the more "flowery/landscaped" backdrops started showing up more in the 1870's and later). You'd also tend to see a faint outline on the tintype caused by the brass mat that covers the image if it was original to the case. Other telltale signs of the approximate date of a tintype can be picked up by the type of plate (thickness, etc.), or from the photo contents (style of clothes, hair, facial hair, hats).
Rob M.
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