Green’s Dictionary of Slang

muff v.1

[ety. unknown; ? image of keeping one’s hands in a SE muff rather than using them properly]

1. (orig. sporting) to make a blunder, to make a mess, to trip up.

[UK]G. Lawrence Guy Livingstone 49: I don’t see why you should have muffed that shot.
[UK]T. Hughes Tom Brown at Oxford (1880) 148: They muffed it in the Gut, eh?
[US]World (N.Y.) 26 July 3/1: On Daly’s muffing Ward’s fourth strike ‘Buck’ crossed the plate.
[UK]‘F. Anstey’ Voces Populi 63: Everyone muffs it at starting.
[US]Ade Girl Proposition 28: After about two Moves she would hand him a Liner which he would Muff.
[UK]N. Gale ‘The Old Professional’ in More Cricket Songs 35: God knows I’ve muffed some easy chances / Of doing good, like a silly lout.
[US]R. Lardner You Know Me Al (1984) 71: The eighth started with Shanks muffing a fly ball off Bodie.
[US]T. Thursday ‘Ten Dollars – No Sense’ in Top-Notch 15 Dec. [Internet] He leaped for it like a greyhound after a bone, fell on his bean, rolled over in the gutter, and grinned. He muffed it by a block.
[US]R.E. Howard ‘Fist and Fang’ Fight Stories May [Internet] You had your chance, and you sure muffed it! I licked you then, and I can lick you now.
J. Archibald ‘Jail, Jail, the Gang’s All Here’ in 10 Detectives Aces Apr. [Internet] The only good crime story in a year and you muff it.
[UK]P. Pringle Boy’s Book of Cricket 68: He [...] muffed it because of the sun in his eyes.
[US]J. Thompson Savage Night (1991) 143: They’d muffed their chance to catch me in the act.
[US]C. Cooper Jr Scene (1996) 105: Davis had told him [...] to make a buy from Bertha Travis, and he had muffed it!
[UK]A. Sillitoe Start in Life (1979) 235: I was being trusted with the big job, and if I muffed it William Hay would get his face bashed in.
[US]N. Pileggi Wiseguy (2001) 161: Our players had to muff enough shots to make sure that they won by less than the bookie’s ten points.
[Aus]E. George ‘I, Richard’ Evidence Exposed (1999) 113: Malcolm had worried a bit that Betsy might muff her role in the ensuing drama.
[UK]Indep. Rev. 25 Feb. 14: Not knowing the jazz progressions / He muffed the middle eight.
[UK]Eve. Standard 13 Apr. 32/1: I totally muffed it.

2. to fail an examination.

[UK]J. Sturgis in Longman’s Mag. III 617: Freddy and Tommy and Dicky have all muffed for the army. It’s really dreadful! [F&H].

3. of a bill, to suffer a default.

[US]T. Thursday ‘Nearly Over’ in Top-Notch 15 Apr. [Internet] He’ll get paid just as soon as some of those dyspeptic editors slip me some coin. It won’t be the first bill he’s muffed.

In derivatives

muffing (n.)

clumsiness, clumsy failure.

[UK]Partridge DSUE (1984) 764: [...] from ca. 1860.
muffing (adj.)

bungling, blundering.

[UK](con. 1840s–50s) H. Mayhew London Labour and London Poor III 54/1: You can pick out a good many Punch performers, without getting one so well versed as I am in it; they in general makes such a muffing concern of it.
[UK]Partridge DSUE (1984) 764: [...] from ca. 1840.

In phrases

muff it (v.)

to die.

[UK]W. Clarke Every Night Book 84: When one of the fancy dies, the survivors say, that he has [...] ‘mizzled’ — ‘morrised’ or ‘muffed it’!