Green’s Dictionary of Slang

knock under v.

[despite Grose (c.1786) and Hotten (1859), knock under, to admit defeat, to submit, is SE]

1. to die.

[UK]Farquhar Sir Harry Wildair IV ii: The Dog was soon gone, knock’d under presently.
‘Hey for the Life of a Soldier’ in Vocal Mag. 2 Jan. 10: Blood and thunder, / Foes knock under, / Then huzza for a victory.
[US]L.H. Medina Nick of the Woods I iii: Tarnal death to the crittur; I’m the man to make him knock under!
[US]H.B. Marriott-Watson Web of the Spider 183: We were all as near knocking under as possible.
[NZ]H.B. Vogel Maori Maid 158: When father knocks under, me and my brother we’ll come into the business.

2. (Aus.) to surpass.

[UK]Satirist (London) 21 Oct. 341/2: Lord PALMERSTON. has given up / His Conferencial thunder, / That roared abroad in Protocols / To knock the Dutchmen under.
[Aus]Bulletin (Sydney) 16 Nov. 14/4: It is all bunkum to say our darkies can’t graft. I’ve seen ’em, in N.S.W. quarries, knock white men under.
[Aus]G. Seagram Bushman All 31: If you don’t knock it [drink] off, it’ll knock you under.