Green’s Dictionary of Slang

mcginnis n.

In phrases

put (the) mcginnis on (v.) (also put (the) macginnis on, ...maginnis...) [SE mcginnis, a wrestling hold]

1. (Aus.) to throttle around the neck.

[Aus]Goulburn Herald (NSW) 20 Dec. 2/5: The villain in the latter instance put on what is termed in their slang, the ‘Maginnis’ pretty strong, as the throat is so much swollen as to almost prevent swallowing.
[Aus]Sydney Sportsman (Surry Hills, NSW) 21 Aug. 4/1: There is no guarantee that his new opponents, the garroters, will not put ‘Maginnis’ on him, half break his neck, and clean his pockets out.

2. (Aus.) to put in a position from which there is no escape, to pressurize; thus crooked maginnis, an unfair form of control, e.g. (moral) blackmail.

[Aus]Stephens & O’Brien Materials for a Dict. of Aus. Sl. [unpub. ms.] 103: MCGINNIS – PUTTING THE, ON: to put any opponent or combatant hors-de-combat. A grip or hold that cannot be unlocked or resisted.
[Aus]Baker Aus. Lang.