The most common and most likely answer to this crossword clue is the 6 letter word ROOFER
I've seen this crossword clue in The Daily Telegraph
R
O
O
F
E
R
Buddy explains!
The straight part
We know that "One offering high-level protection" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case one offering high-level protection = roofer.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 ROOFER mean?
ROOFER noun- A craftsman who lays, or repairs roofs.
- A daredevil who performs stunts on tops of skyscrapers.