bunion derby, n. — Green’s Dictionary of Slang

bunion derby n.

[SE bunion + The Derby, a well-known horserace in the UK and as the Kentucky Derby in the US]

(US) a cross-country marathon.

1928		New Yorker 8 Dec. 31: C.C. Pyle [...] invented the bunion derby and lured [...] Red Grange and Suzanne Lenglen into the gilded cage of professionalism.
1999		Wilbraham & Monson Academy 🌐 On Tuesday, November 16, the faculty and students of Wilbraham & Monson Academy once again celebrated the end of the fall trimester with the Bunion Derby.
2001		John Loeschhorn’s Running Lifestyle 🌐 In August of 1991 I learned that the first transcontinental footrace since the Bunion Derby of 1929 would be contested in 1992.