The most common and most likely answer to this crossword clue is the 8 letter word DRAMATIC
I've seen this crossword clue in The Guardian
D
R
A
M
A
T
I
C
More clues leading to the result DRAMATIC
- Very severe, with mother replacing son — striking
- Striking a flowing boundary up in Durham — it leads to century
- People are keen take part in such a society
- Drive Nancy’s friend around at 100? That’s impressive
- Most people want to take part in such society
- A jerk carrying some whisky? That’s unexpected
- Sort of society in which people want to take part?
- Thespian having Scotch maybe, and a second unfinished
- Striking play needing endless credit
- Striking a nervous response after short measure
Buddy explains!

The straight part
We know that "unexpected" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case unexpected = dramatic.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 DRAMATIC mean?
DRAMATIC adjective- Of or relating to the drama.
- Striking in appearance or effect.
- Having a powerful, expressive singing voice.