The most common and most likely answer to this crossword clue is the 6 letter word CORDON
I've seen this crossword clue in The Daily Telegraph
C
O
R
D
O
N
Buddy explains!
The straight part
We know that "barrier" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case barrier = cordon.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 CORDON mean?
CORDON noun- A ribbon normally worn diagonally across the chest as a decoration or insignia of rank etc.
- A line of people or things placed around an area to enclose or protect it.
- The arc of fielders on the off side, behind the batsman - the slips and gully.
- A woody plant, such as a fruit tree, pruned and trained to grow as a single stem on a support.