The most common and most likely answer to this crossword clue is the 7 plus 4 letter word MARTIAL ARTS
I've seen this crossword clue in The Daily Telegraph
M
A
R
T
I
A
L
A
R
T
S
More clues leading to the result MARTIAL ARTS
Buddy explains!
The straight part
We know that "methods of self-defence" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case methods of self-defence = martial arts.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.