The most common and most likely answer to this crossword clue is the 8 letter word THUGGERY
I've seen this crossword clue in The Daily Telegraph
T
H
U
G
G
E
R
Y
More clues leading to the result THUGGERY
- Bullying bear, supposedly, in heartless Tory
- Hear about embrace, say, having backed violence
- Violent behaviour almost embraced during endeavour
- Thank you initially for embracing embracer with brutal violence
- Take to court, involving one embracing mostly violent activity
- Violence in outskirts of Turkey, within which one getting a grip?
- Violence, as bear enters outskirts of Torquay
- Try huge walkabout round middle of jungles to see gorillas’ behaviour?
- Violent behaviour in tower across hotel yard
- Threats and violence in attempt to conceal goods in shade
Buddy explains!

The straight part
We know that "Violent behaviour" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case violent behaviour = thuggery.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 THUGGERY mean?
THUGGERY noun- The violent, criminal acts that are associated with thugs, and/or the fashion, manner of speaking, and demeanor associated with them.