"Football" is an American recasting / misunderstanding of the Gaelic "usquebaugh" (sp?), meaning whiskey. There were a good many native Irishmen and other Gaelic speakers fighting in the Civil War.

I think I may have provided this in another thread, but it's worth repeating. I collected a version called "Skebaugh" from Ben C. Moomaw near Hot Springs, VA 1955, as follows, to a tune that's a major-key variant of the minor-key When Johnny Comes Marching Home tune:

SKEBAUGH

In eighteen hundred and sixty-one,
Skebaugh, says I,
In eighteen hundred and sixty-one,
Skebaugh, says I,
In eighteen hundred and sixty-one
We licked the Yankees at Bull Run,
And we'll all drink stone blind,
Johnny come fill up the bowl.

In eighteen hundred and sixty-two...
We licked the Yankees through and through...

...sixty-three...
Old Lincoln set the darkies free...

...sixty-four...
I said I'd fight this war no more...

...sixty-five...
We thanked the Lord we were alive...