re Hole in the Wall:

Uncle Dave Macon has a line in his riverboatman's ditty Rock About My Saro Jane:

Engine give a [my memory: "crack," may be incorrect], whistle give a squall,
Engineer gone to the hole in the wall, And a- Oh, Saro Jane.

I think I have seen the Hole in the Wall explained as a place where you get liquor, perhaps the name of a dive. But also at one point people got their liquor in takeout fashion, bringing a "can" -- a metal pitcher or tankard -- to the source of the stuff. They took their cans down the street to be filled by measure, just as we go to the liquor store and get a pint or a fifth. They may originally have paid through a shuttered hole in the wall just as we today get takeout through a takeout window, without having to go inside the building.

The liquor dispenser, often a barrel with a tap, was sometimes called a "growler" because it made a growling noise when the tap was running. (Experts in the matter please correct any wrong details -- that's my understanding from what I've heard and read.)

The only song reference to this I'm aware of comes in the old silly song "Fireman Save My Child" -- found in Sandburg's American Songbag:

There was a little man and he had a little can,
And he used to rush the growler...

Just how Ten Broeck beat Molly at the hole in the wall I'm not sure, but at a guess, race results may have been posted in bars (just as they later were by Western Union ticker in various commercial locations) and informally related by the bartender at a local growler along with the takeout booze.

Or perhaps it really was the name of a local dive, and race results were reported there, just as today we go and watch the race in a bar on TV? Other possibilities welcomed.

Bob