The most common and most likely answer to this crossword clue is the 8 letter word POWERFUL
I've seen this crossword clue in The Daily Telegraph
P
O
W
E
R
F
U
L
More clues leading to the result POWERFUL
Buddy explains!

The straight part
We know that "Violent" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case violent = powerful.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 POWERFUL mean?
POWERFUL adjective- Having, or capable of exerting power, potency or influence.
- Large; capacious; said of veins of ore.
- To a great extent or degree.
- Conforming to fact, reality or rule; true.
- (with superlatives) Used to firmly establish that nothing else surpasses in some respect.