The most common and most likely answer to this crossword clue is the 8 letter word UPRIGHTS
I've seen this crossword clue in The Guardian
U
P
R
I
G
H
T
S
More clues leading to the result UPRIGHTS
Buddy explains!

The straight part
We know that "Posts" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case posts = uprights.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 UPRIGHTS mean?
UPRIGHTS noun- Any vertical part of a structure, especially one of the goal posts in sports.
- A word clued by the successive initial, middle, or final letters of the cross-lights in a double acrostic or triple acrostic.
- An upright piano.
- Short for upright vacuum cleaner.