Green’s Dictionary of Slang

el foldo n.

also el floppo
[cod Sp.; el- pfx + fold v. (7)]

(US) a failure, a flop, esp. in sport or a feigned knockout in boxing.

[US]N.Y. Times 5 Dec. 10: [headline] The Grandest El Foldo. Maxwell Stiles, football writer in The Los Angeles Examiner, said: [...] ‘Of all the teams that ever played at Pasadena, Pitt has consistently done the grandest el foldo.’.
[US] in W.C. Fields By Himself (1974) 173: After doing an el floppo as a writer, you are back in dear old Kansas City telling what is wrong with pictures.
[US] ‘Whitman College Sl.’ in AS XVIII:2 Apr. 154/1: el foldo. Failure to make the grade.
[US]B. Schulberg Harder They Fall (1971) 191: I’ll come [...] but I’ll still tab it for an El Foldo.
[US]S. Longstreet Flesh Peddlers (1964) 51: I [...] rode for the Baker Brothers Show till it went el-foldo.
posting at Sons of Sam Horn 9 Aug. 🌐 What the hell is up with the Angels winning ten in a row? When is their el foldo going to start?

In phrases

pull an el foldo (v.) (also pull an el floppo)

(US) to collapse, to give in.

[US]J. Thompson ‘Sunrise at Midnight’ in Fireworks (1988) 162: My information is that you have a piece of Gwaltney [i.e. a boxer] and he pulled an el floppo on orders from you.
A. Rahn ‘Gymnastics rolls by UCLA’ in Arizona Daily Wildcat 29 Jan. 🌐 That has pretty much been the pattern this year. We hit vault and bars strong, but then pull an el-foldo on the beam.