ONLY-FLIES-STRAIGHT GOLF BALL

[Migg]

my original post was inspired by a sports article about golf. The first paragraph runs like:

"If you're like me, your tee shots have a tendency to shoot into the woods faster than a scalded dog. Fear not, friends, there's a cure for all of us, as the New York Times tells us: a new, only-flies-straight golf ball! There's just one small catch ..."



In the first paragraph, the phrase "a new, only-flies-straight golf ball" was used. Why is the plain form of "fly" not used in the modifier position?

[konungursvia]

3rd person singular: It flies.

[Migg]

could anyone offer more advice on verb phrase premodifiers?