Green’s Dictionary of Slang

any form of evasive story or trick.

1812		Vaux Vocab. of the Flash Lang. in McLachlan (1964) 269: stall off: a term variously applied; generally it means a pretence, excuse, or prevarication—as a person charged with any fault, entering into some plausible story, to excuse himself, his hearers or accusers would say, O yes, that’s a good stall off.
1846		Swell’s Night Guide 76: She gammons to fake her smalls vith the vite vipe; but its a stall off to mop the pawney out of her blinkers.
1859, 1860		Hotten Dict. of Modern Sl. etc.
1861		(con. 1840s–50s) H. Mayhew London Labour and London Poor I 424/1: There’re plenty of travelling women who go about with a basket and a bit of driss (lace) in it, gammy lace, for a stall-off (a blind), in case they meet the master, who would order them off.
1881		Newcastle Courant 2 Dec. 6/6: ‘I’ll take the snow up[ as a stall off .’ [...] He took a basket of clean clothes.