Mephisto. Help With Parse Please

[Bozzer]

In New Orleans you all shout America’s first-for eccentricity.
Answer is Yall.
I can see it is “American” for You All but what’s it got to do with eccentricity?

[Spoffy]

YELL ('shout'|) with A ('America's first') for E (eccentricity, abbreviation)

[Bozzer]

Thank you. Is E really an abbreviation for eccentricity or just the first letter?
Anyway the clues are all in and I am indulging in a highly modified saloop of Bells and ginger.

[Neveracrossword]

Chambers gives 'e: the eccentricity of a conic section'.

[fiction-factory]

E for eccentricity in Science- to do with orbital properties I recall

[fiction-factory]

https://en.wikipedia.org/wiki/Orbital_eccentricity

[Neveracrossword]

I quoted Chambers as it's used in crosswords.

[fiction-factory]

I quoted my own recollection of studying eccentricity in maths/science years ago. I wasn't doubting yours, NAXW- it wasn't there when I started typing. yes, Chambers is the bible usually

[Bozzer]

Thank you again. That is such a wonderfully obscure bit of esoterica (to a non mathematician) that I shall remember it for ever! I am glad I asked.

[Neveracrossword]

And I'm glad you asked, Bozzer - in many years of crossword-solving, I don't think I've seen 'e = eccentricity' before. I checked Chambers speculatively!