The most common and most likely answer to this crossword clue is the 8 letter word PACIFISM
I've seen this crossword clue in Financial Times
P
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More clues leading to the result PACIFISM
Buddy explains!

The straight part
We know that "non-violent way" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case non-violent way = pacifism.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 PACIFISM mean?
PACIFISM noun- The conviction that it is morally wrong to settle disputes (especially between countries) by war or other violent means.
- The additional challenge of winning a game without attacking any enemy characters.