Green’s Dictionary of Slang

(US Und.) very strong, and prob. adulterated liquor.

1928		Phila. Eve. Bulletin 5 Oct. 40/3: Here are a few more terms and definitions from the ‘Racket’ vocabulary: [...] ‘block-and-fall,’ very strong and doubtful liquor.
1932		I. Einstein Prohibition Agent No. 1 240: There was a kind of bargain stuff called ‘block-fall’ which certainly did live up to its name – you took a drink of it, walked a block, and fell. And from the samples I collected I’d say it was guaranteed.
1941		M. Prenner ‘Drunk in Sl.’ in AS XVI:1 Jan. 70/2: liquor [...] block and fall [i.e. drink walk a block and fall down].