Green’s Dictionary of Slang

(US) completely, overwhelmingly, usu. of defeat.

1918		H. Simon ‘Prison Dict.’ in AS VIII:3 (1933) 25/2: COLDCOCK. [...] 2, adverbial objective, as in So I up an’ knocked ’im cold cock.
1978		S. King Stand (1990) 235: Beggars couldn’t be choosers. They had him cold-cocked anyway.
1982		W. Wharton Midnight Clear 111: Krauts jumped us, had us cold cock [...] then didn’t shoot.