The most common and most likely answer to this crossword clue is the 9 plus 5 letter word EMERGENCY BRAKE
E
M
E
R
G
E
N
C
Y
B
R
A
K
E
Buddy explains!
The straight part
We know that "Back-up for safety" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case back-up for safety = emergency brake.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.