Of American-English origin, the colloquial noun knuckle-sandwich denotes a punch to the mouth (or to the stomach—cf. below, quotation from the Daily Mirror (London, England) of 2nd July 1963).
The image is of a sandwich of knuckles being forced into the mouth (or into the stomach) of the person who is punched.
The earliest occurrence of the noun knuckle-sandwich that I have found is from the caption to the following photograph, published in the San Francisco Chronicle (San Francisco, California) of Monday 19th August 1940:
LIKE A BEEF?
HOW’D YA LIKE A KNUCKLE SANDWICH, PARD? Fightin’ Bob Jensen, the huge Seal rookie hurler, who came within 25 yards of knocking Hollywood’s Jack Rothrock’s noggin into the bleachers Saturday, gives Pard Ballou a sample of the Jensen jolt in the dugout during yesterday’s Seal-Star divide. Fightin’ Bob, who isn’t an ugly so-and-so as Rothrock claimed, started after the Hollywoodian and would have engaged him in a “white hope” fisticuff had not first baseman Ferrie Fain cooled him off. As for Ballou, Jensen can go pick on somebody his own size.
The noun knuckle-sandwich then occurs in the following from The Chicago Sun (Chicago, Illinois) of Saturday 21st November 1942:
Wildcats, Irish Knuckle Down to Business Today
More Than Footballs May Fly in Grid Game; Score Usually Close
By Edgar Munzel.
South Bend, Ind., Nov. 20.—Northwestern and Notre Dame, which combine year after year in serving one of the top football dishes of the country, will clash here before 35,000 tomorrow afternoon in the 22d revival of the feud.
What is known in football culinary vernacular as a “knuckle sandwich” as usual will be one of the traditional side dishes on the menu. In the midst of the bruising battle these arch rivals have frequently been suspected of throwing the football out of the contest and just going at it with fists, knees and elbows and the devil take the hindmost.
BRITISH ENGLISH: KNUCKLE-SANDWICH AND KNUCKLE-BUTTY
The noun knuckle-sandwich has been borrowed into British English. The earliest occurrence that I have found is from an article by Ed Vale about “allegations of brutality at the training depot of the crack Brigade of Guards”, at Pirbright, Surrey—article published in the Daily Mirror (London, England) of Tuesday 2nd July 1963:
Recruits at Pirbright had alleged that they were subjected to “extreme bullying.”
Some of the recruits spoke to me of:
“Betsy”—a nickname for blows on the back of the head with a rifle butt;
“Knuckle-sandwiches”—another nickname to describe what recruits say are punches in the stomach; and
“Forearm smashes”—a wrestling blow delivered with the arm across the face or body.
A variant, knuckle-butty, is used in Lancashire, a county of north-western England, on the Irish Sea. The earliest occurrence that I have found is, as knuckle buttie, from Yennoworrameanlike (Liverpool: Raven Books, 1972), a collection of poetry by the Liverpudlian author James Brian Jacques (1939-2011)—as quoted by Tony Crowley in The Liverpool English Dictionary: A Record of the Language of Liverpool 1850—2015 on Historical Principles (Liverpool: Liverpool University Press, 2017).
The noun knuckle-butty then occurs in Mike Harding 1 in Stockport, by Barry Coleman, published in The Guardian (Manchester, Lancashire, England) of Monday 25th June 1973:
Harding is a folk singer and most of his material deals with life in the industrial North, and in particular Manchester. […]
A recurring theme of Harding’s is his birthplace Crumpsall 2. He remembers life behind the dark satanic cream cracker factory where the kids played in gas masks and his family was so poor they used to sell pegs to the gypsies. He admired the people who went shopping in Kendal Milnes without getting found out. “Ah Crumpsall,” he sighs, “the place that makes Rotherham look like Las Vegas.”
In spite of the dye factory and the clogs, Harding clearly loves his subject. He can say what he likes about Crumpsall. Anyone else with too much to say might be well on the way to a knuckle butty. Know wharra mean?
1 Mike Harding (born 1944) is a British singer, songwriter, comedian, author, poet, broadcaster and multi-instrumentalist.
2 Crumpsall is a suburb of Manchester, a city historically situated in Lancashire.
AUSTRALIAN ENGLISH: KNUCKLE SANDWICH
The noun knuckle-sandwich has been borrowed into Australian English. The earliest occurrence that I have found is from Norm and Ahmed (first performed in 1968), by the Australian playwright Alexander Buzo (1944-2006)—as quoted in an article on censorship, published in Tharunka 3 (Kensington, New South Wales) of Tuesday 21st April 1970:
I remember one bloke. A real coot. Played prop for Balmain juniors. Tall bloke, he was. A long thin streak of pelican shit. He tried to hang one on me at Leichhardt Oval once, so I administered a knuckle sandwich to him.
3 Tharunka: the Journal of the University of New South Wales Students’ Union.