The most common and most likely answer to this crossword clue is the 8 letter word IMMUNITY
I've seen this crossword clue in The Guardian
I
M
M
U
N
I
T
Y
More clues leading to the result IMMUNITY
Buddy explains!

The straight part
We know that "Protection" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case protection = immunity.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 IMMUNITY mean?
IMMUNITY noun- The state of being insusceptible to something; notably:
- A resistance to a specific thing.