Green’s Dictionary of Slang

1. to strike, to hit on the head.

1841		C.H. Hartshorne Salopia Antiqua 517: Nobler, a man whose duty it is to remind inattentive youths in church, of their misbehaviour, by ‘nobling’ them, or hitting them on the head with a wand .
1847		‘Epistle from Joe Muggins’s Dog’ in Era (London) 14 Feb. 3/2: [N]otwithstanding the new act against dog stealing, I had been ‘nobbled,’ and knocked on the head.

2. to kill.

1976		P. Theroux Family Arsenal 168: ‘I saw a bloke nobbled here,’ she said. ‘I mean killed.’.
1983		A. Payne ‘Get Daley!’ Minder [TV script] 55: Well, he must have been at the warehouse when Harrison got nobbled.