Green’s Dictionary of Slang

1. to find, to observe, to watch, to discover.

1742		Ordinary of Newgate His Account 22 Nov. 18/1: Thereupon Jennings said to Peterson, come away Jack, he has stagg’d us.
1745		Proc. Old Bailey 30 May 159/1: Jeffs said to Mr. Tawney, D – n your eyes, what do you stag at? and then Jeffs said to Martin, D--n your eyes, kiddy flash away.
1753		J. Poulter Discoveries (1774) 43: He stags my Muns; he knows my Face.
1754		G. Stevens ‘A Cant Song’ Muses Delight 177: As I trolled a-long I grappled her shell, she stag’d rum bowman and knew me full well.
1770		Cheats of London Exposed 12: When a stranger enters the room, they all, to use their own phrase, stag him [...] and discern if he is a pidgeon.
1788		‘Rolling Blossom’ in Festival of Anacreon in Wardroper Lovers, Rakers and Rogues (1995) 179: When Phil the flat had stagged my charms / He swore none else could please him.
1789		Merry Fellow’s Companion 28: ‘[A]s I was coming by the corner of the street, I stagged the man’.
a.1790		H.T. Potter New Dict. Cant (1795) n.p.: stagg’d seen, observed, discovered.
1796		Sporting Mag. Aug. VIII 252/2: Stag what may happen if we should be queer’d of a reform.
1802		M. & R. Lovell Edgeworth Essays on Irish Bulls 138: Why, I was down upon him [...] I mean, my lord, as deep as he thought himself, I stagged him.
1809		G. Andrewes Dict. Sl. and Cant [as cit. 1753].
1818		W. Perry London Guide 13: [If] the transaction may have been ‘stagged’ by some impertinent bystander or a trap, he [...] drives away.
1824		‘Sonnets for the Fancy’ in Egan Boxiana III 621: And thus they sometimes stagg’d a precious go. / In Smithfield, too, where graziers’ flats resort.
c.1830		‘Unfortunate Billy’ in Holloway & Black I (1975) 268: Till leering Nan and Teddy Blink, / Had stagg’d the knowing laddy.
1832		J. Miller Complete Jest Book 261: As I was coming round the corner of the street, I stagged the man.
1846		Swell’s Night Guide 59: Stag here – pipe this donna and swell paddling here.
1855		Broadway Belle (NY) 1 Jan. n.p.: I’ll get me gone, and stag your knibbs from a distance.
1859		H. Kingsley Recollections of G. Hamlyn (1891) 26: So you’ve been stagging this gentleman and me, and listening, have you?
1864, 1867, 1870		Hotten Sl. Dict. 244: stag to see, discover, or watch; ‘Stag the push,’ look at the crowd.
1873		Sl. Dict.
1876		St Louis Globe-Democrat 19 Jan. n.p.: This excites merriment, and they all say, ’stag his nibs’ while one waxes confidential, and asks, ‘how are you fixed?’.
1882		Sydney Sl. Dict. 9/2: Kino, the macing cove, kidded on a dollymop where the bloak’s got a swag of sheen. Kino’s cocum, and he’s stagging to crack the crib. Kino, the housebreaker, enticed a servant-girl (to keep his company) where the master has a quantity of plate. Kino’s wary, and he is watching to break into the house.
1895		Crowe Aus. Sl. Dict. 80: Stag, [...] to discover,‘stag the push,’ ‘look at the crowd’.
1891		F.W. Carew Autobiog. of a Gipsey 412: Did you stag the milingtary-lookin’ swell with the ’starchios and Piccadilly-veepers.
1907		Dundee Courier 4 Nov. 8/1: I stagged him in a moment [...] when I say I was up to him and down to him [...] that I saw he was a rum kiddy so I gave him one on the tibby.

2. to inform against.

1819		P. Egan Key to the Picture of the Fancy going to a Fight 14: To those [...] who do not wish to be stagged by their customers as going to a mill.
1821		‘An Amateur’ Real Life in London I 316: He was up to his gossip,—that he stagged him, for he was not to be done.
1835		G. Kent Modern Flash Dict.
1846		Leeds Mercury 4 Apr. 7/5: [Tipperary Assizes, Ireland] Well, my fine boy, when did you turn informer? [...] When did you split, or burst as they say in the Terry slang — when did you stag?
1848		Flash Dict. in Sinks of London Laid Open.
1859		Matsell Vocabulum.
1963		L. Daiken Out Goes She 12: Let the traitor tell, stag, sneak on his fellows, and he will not do it twice.
1981		(con. 1920s) P. Crosbie Your Dinner’s Poured Out! 220: to stag to betray.