The most common and most likely answer to this crossword clue is the 8 letter word ACROSTIC
I've seen this crossword clue in Independent
A
C
R
O
S
T
I
C
More clues leading to the result ACROSTIC
- Word puzzle bringing on a vexed moment, by the sound of it
- A pair of short teachers' marks for poem?
- A cold potato dish initially caused a puzzle
- An oblique sign of approval aired for puzzle
- Puzzle given a couple of marks for wrong and right answers, we hear
- Angry for the most part being grabbed by a jerk? That’s puzzling!
- A clue-type relying on structure: this illustrative clue primarily?
- Working actor’s introductions to Independent’s crossword puzzle
- And next – Clue text – Right here? – Oh dear! – Stand out – To shout – I think – Clue stinks!
- At initial reading this verse has extra meaning
Buddy explains!

The straight part
We know that "(something) that’s puzzling" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case (something) that’s puzzling = acrostic.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 ACROSTIC mean?
ACROSTIC noun- A poem or other text in which certain letters, often the first in each line, spell out a name or message.
- A poem in Hebrew in which successive lines or verses start with consecutive letters of the alphabet.
- A kind of word puzzle, the solution of which forms an anagram of a quotation, and their initials often forming the name of its author.