The most common and most likely answer to this crossword clue is the 6 letter word KICKER
I've seen this crossword clue in The Guardian
K
I
C
K
E
R
More clues leading to the result KICKER
Buddy explains!

The straight part
We know that "Unexpected twist in US" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case unexpected twist in us = kicker.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does KICKER mean?
KICKER noun- One who kicks.
- One who takes kicks.
- The kicking strap.
- An outboard motor.
- An unexpected situation, detail or circumstance, often unpleasant.
- An enticement for investors, e.g. warranty added to the investment contract.
- An unpaired card which is part of a pair, two pair, or three of a kind poker hand.
- Small text above a headline that indicates the topic of the story.
- The last one or two paragraphs of a story.
- A lighthearted or humorous item used to round off a news broadcast.
- A device that periodically displaces a newspaper from the print production line, to aid in gathering the newspapers into fixed-size bundles.
- A launch ramp.
- The fermenting mass of fruit that is the basis of pruno, or "prison wine".
- A relaxed party.
- A backlight positioned at an angle.
- An introduction; something that leads into the beginning of something.
- A region of data at the beginning of a compact disc, holding the table of contents.
- A short phrase that begins the caption of a photograph.
- A particular type of Texan who is associated with country/western attire, attitudes and/or philosophy.