Green’s Dictionary of Slang

ricket n.

[ety. unknown; link to the disease SE rickets]

a mistake, a blunder.

[UK]F. Norman Fings I i: For once in yer life you didn’t make a ricket. It won all right, look.
[UK]F. Norman Guntz 193: That was the biggest ricket I made.
[UK]‘P.B. Yuill’ Hazell and the Three-card Trick (1977) 59: Sorry mate, I must have made a ricket there.