The most common and most likely answer to this crossword clue is the 9 letter word AFTERMOST
I've seen this crossword clue in The Daily Telegraph
A
F
T
E
R
M
O
S
T
More clues leading to the result AFTERMOST
Buddy explains!

The straight part
We know that "Right at the back" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case right at the back = aftermost.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 AFTERMOST mean?
AFTERMOST adjective- Nearest the stern of a vessel; hindmost.