Noted in a NYT story on the 4th, the N + N compound crap game ‘game of craps’. I was reminded of the line from Guys and Dolls:
But for the good old reliable Nathan, oh it’s only just a short walk,
To the oldest established permanent floating crap game in New Yawk.
(or New York, if you insist on a standard pronunciation).
Street craps in a studio theatre performance of Guys and Dolls
Now the name of the game is craps (never crap), which is PL in form (apparently having the Z suffix of the PL) but strictly SG syntactically: Craps is / *are a fascinating game. Nevertheless, as N1 in a N + N compound, the word can appear in a formally SG variant, crap — as well as in its formally PL variant: craps game is entirely acceptable.
This variation, between formally SG and formally PL in N1, is well-known (under the heading “plurals in compounds”, the name echoing the standard assumption that N1 should be formally SG) but is much more widespread than people have been inclined to think. Crap game alongside craps game is just another example among many — but it turns out to fall in with a whole set of examples, involving game names that are formally PL.
A side issue is the origin of the name craps, which is very much unclear. The OED has one speculation (so labeled) on the matter, and the Wikipedia article on the game has another (a plausible story, taken from a 1938 popular history of gambling in America, that might be sheer invention).