Green’s Dictionary of Slang

Injun v.

[derog. association of Injun n.]

to creep up on, to ambush.

[US]W.H. Thomes Bushrangers 65: ‘Gol darn their pictures!’ cried Hez, who had crawled on his stomach until he had struck a blow for my relief; ‘didn’t I Injun ’em that time?’.
[US]A.H. Lewis Wolfville 29: While she’s gone I injuns an’ spies ’round a whole lot.