The most common and most likely answer to this crossword clue is the 6 letter word SUNHAT
I've seen this crossword clue in The Daily Telegraph
S
U
N
H
A
T
Buddy explains!

The straight part
We know that "high-level protection" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case high-level protection = sunhat.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 SUNHAT mean?
SUNHAT noun- A light, wide-brimmed hat to protect from the sun.