The most common and most likely answer to this crossword clue is the 3 plus 3 letter word PEG OUT
I've seen this crossword clue in The Guardian
P
E
G
O
U
T
More clues leading to the result PEG OUT
Buddy explains!

The straight part
We know that "to finish at 1 down" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case to finish at 1 down = peg out.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.