Green’s Dictionary of Slang

1. a blow or punch.

1937–84

Partridge DSUE (1984) 400/2: ca. 1860–1910.

2. a verbal response.

1937–84

Partridge DSUE (1984) 400/2: ca. 1860–1910.

3. (orig. milit.) a trick, a swindle, a hoax; thus do/pull/work a flanker v., to trick, to swindle.

1923		J. Manchon Le Slang.
1975		‘P.B. Yuill’ Hazell and the Three-card Trick (1977) 143: It was just crossing my mind she might still be planning a flanker.
1989		J. Morton Lowspeak 150: Work a flanker – to obtain by stealth or a trick.
1997		N. Barlay Curvy Lovebox 140: Pull a flanker an’ you know what you’ll get.
2001		I. Rankin Falls 28: It was just the local evening paper trying to pull a flanker.