What's the proper grammar for this? It seems like a perfectly acceptable order for the words, but you're right that there's some flow missing. Commas surrounding 'Saturday' perhaps?

I'm guessing "...threatened on Saturday..." is probably a better way to phrase it

It's a better way to phrase it, certainly, but that wasn't my question. I've heard reporters use the original phrasing (i.e. "threatened Saturday"), so I consider it correct, just with incorrect punctuation. I was trying to figure out what the proper punctuation would be without changing the words.

This is part of a more general problem I have with being able to write the way I speak. I don't think I have terrible grammar when writing something relatively formal, in a "written tone" rather than a "spoken tone", but when I make comments on reddit or HN, I've noticed I have a general inability to also make my writing grammatically correct. I also use a lot of parentheses, because I tend to talk in tangents, and that's the only way I can really write it that makes sense.

It was an intellectual curiosity, nothing more.

I assume you're aware of this? It might appeal...

http://en.wikipedia.org/wiki/Buffalo_buffalo_Buffalo_buffalo...

It's not really grammatically sound, but rather a result of shortening the phrase/sentence while still making sense.

The original and the version with the added preposition are both correct. If there were a real ambiguity you'd favor the preposition, but that isn't the case here.

British English requires the preposition.

It doesn't. You can easily see this by searching British media for the phrase "said Thursday" or the like. It's the same construction.

https://www.google.com/search?hl=en&client=firefox-a&...

"...threatened on Saturday..."

nonsense.